Yep, that was it.  The Cosm library requires the HttpClient library to work.  The url of the library is in the Cosm README file.

Take a look at the README file, there is another library you have to get. 

I use Cosm, but not the library.  I recently moved some code I have to IDE 1.0.3 and had a bunch of trouble compiling various things because I needed to change an #include.  It needs to change from WProgram.h to Arduino.h .

I suspect you're having the same problem.  Look through the library and see if this is the case.

Let's see, the speed of light is something 300 million meters/second.  So, the maximum range of an XBee is about 300 meters, so you should see about 1 millionth of a second pass one way and another coming back for transmission time.  As far a RSSI goes, it varies a lot based on what's between the two XBees and how that whatever changes from one transmission to the next.  Set two of them 30 meters apart in the middle of the desert and you'll have a reading that varies as the wind blows.  I know, I live in the middle of the desert.

There just isn't any way to actually measure how far apart two XBees are aside from hooking each of them to a GPS, and then only if you have a really good GPS.

I've been where you are and made a bunch of mistakes, so a couple of suggestions:  I like this board for an XBee shield

http://www.ebay.com/itm/XBee-shield-for-Arduino-/220982906382?ssPageName=ADME:L:OC:US:3160

It lets you connect the serial input on the XBee to any pin on the arduino, and if you use a mega2560, you add a couple of wires and can get to any pin on it as well.  It has leds, reset switch, and prototype area so you can mess around a bit on the board itself.  You can piggy back another shield on top of it also.

As for sensors, visit Terry King's site at http://arduino-direct.com/sunshop/ , he has a bunch of sensors, shields, and most importantly, examples of using a lot of the stuff.  Even though you already have some items, the articles and description of the devices will help you understand how this stuff works.

XBee, I didn't see where you mentioned which XBee you got, but I hope it's a Series 2 or 2.5 device.  The series 1 are marginally easier to use, but they don't have anywhere near the capabilities of the later devices.

To get you started, decide what you want to do.  Maybe measure the temperature in your main room.  For this you need a temperature sensor to plug into the arduino.  Then you will want to see what it's reading, so you'll probably want to get an LCD display.  Then you'll want to do something else.  As you decide what you want to monitor or control, you'll understand what you need to have to do it.

As for multiple sensors, yes you can have multiple sensors.  The arduino can sample a number of them and then format a message to send through the XBee to another one hooked to some device you want to get the data to.

Basically, think about what you want to do, gather some information on doing it, then go have fun.

You're right, I missed it.

In the link

Nice job.  How hard was the android app?

Typo maybe??  I found the F() macro explained at http://arduino.cc/en/Main/ReleaseNotes

Keep this in mind for the future.  It doesn't have to be three exclamation points in a text string.  I had it happen with data I had typed into an array in hex.  Took me forever to find the problem and I knew about the !!! problem.  If you decide to bite the bullet and replace the bootloader, I have a page on this on my blog at http://www.desert-home.com/2012/05/arduino-mega2560-wrapping-up-bootloader.html

This particular bootloader fixes watchdog timer also.

There's a bunch of experts at reading pulses and other stuff from a meter over at http://openenergymonitor.org that you can consult with on this.  Also, if you use software serial in its latest incarnation, you can read reverse signals on the serial input.  This allows you to use the regular serial as a monitor or command port.  The page for it is at http://www.pjrc.com/teensy/td_libs_AltSoftSerial.html  I haven't used it with signal inversion, so you'll have to take a look at the library to see how to set it up for this.  More info on this at http://arduiniana.org/libraries/newsoftserial/

I tried reading my meter which gives out red (can you believe it) pulses.  I was getting terrible interference from ambient light and had to get some modeling clay and mash it all over the sensor and about an inch out to the side.  This gave me enough signal to reliably count pulses, but the clay melted in the sun and I haven't gone back to the project to see what is better to do.  Took about an hour to clean up the melted clay from the meter and the concrete under it.  There are lots of silicon based solutions that I could have used, but I happened to have some dark blue clay.....  When you get that far along, google oogoo for a material that works really well for stuff like this, you can even tint it to the color you need.

That is so weird.  Znet 2.5 is supposedly retired in favor  of Zigbee.  The series 2b modules aren't even supposed to be able run that software.  Or, I've managed to get it totally wrong somehow.

Nope, the smoke got clean away.  And Yes, it will work great with a 24VDC supply.  Those little buck supplies are great.

It really is brilliant.  The problem is that now that the idea has been published on kickstarter, there will be a few hundred of them on the market produced by entrepreneurs in low labor cost areas for a dime or so (probably with subsidized free shipping)

The problem I had with a buck converter was that it was rated like the one Lefty pointed out with a max input of 35VDC.  When you rectify and lightly filter a 24VAC supply, it comes out around 37VDC which is just over the max for the buck converter.  In my case I tried two of them, neither one was the one Lefty indicated, and they both got hot and failed in a couple of days.

Lefty may have tried the one he shows at that level and had a good experience, but I had both of mine release small amounts of magic blue smoke.  They didn't work too well after that.  You might have better luck looking around for one that can handle 40VDC or better input to give you a fighting chance of a reasonable lifetime.