Some people still have non-Intel Macs, and the new OSX:s are made for Intel only, not for PPC. That's why.

If a Retail-copy of the Leopard (10.5) install disk can be found, it will work on PPC based Macs.  Snow Leopard (10.6) was the first to strip all PPC support.

when I go into my network preferences it says "arduino uno is configured, but is not connected

OSX sees the UNO as a modem.  Nothing in the network prefereces matter, except that it shows up as a device.  "connected" in this sense refers to a modem bring connected to anther modem.  NOT that the "Arduino is connected."

Also, should I be changing the lines of code to reflect the changed baud rate. Meaning will the code run less optimally if not set right?

Err, the code will run the same regardless of what the baud rate is set to.  The only difference is sending will either be faster or slower, depending on what the baud rate is.  

The Serial.begin(x) needs to be the same baud rate you are using on your computer.  Otherwise, they probably can't talk to each other.

When plugged in, does the FTDI chip get warm?  It is what communicates with your PC, not the ATmega328.

You might also check the 3v3 line, since it is generated by the FTDI.

I just used the Arduino.cc search for "Windows 64bit" and found this:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1286667057/9

Look near the bottom.

If you search for the error, you'll generally find auto-reset isn't working.

Try pressing and holding the reset button until about 1 second after the "Sketch is xxxx size" message.

Notice how only certain words are highlighted and not the ".h"?  The highlighting is a result of the IDE editor's relatively simple syntax highlighting.  The words in Orange are known and have other functions.  In this case, it has nothing to do with being libraries.

Look at the EEPROM library.  There is a small amount of EEPROM available to store things like integers.  You could increment a "state variable" in the EEPROM each time the sketch first runs or resets.  

http://www.arduino.cc/en/Reference/EEPROM

Without any schematics, links to the hardware you are using, code, or a list of what you have tried (along with the exact outcome:  "it didn't work" doesn't count) there are not many suggestions to give.

Search the forum for your errors.  Plenty of suggestions and ideas in other threads.

I'm guessing that means it's consuming 4 micro amps, which, even with 15 shift registers, shouldn't cause an issue since the total load is a single LED plus the registers.

Depends on who's shift register you are using.  For example, TI's is rated for 80uA.  That's still a small amount of current.  However, don't forget that whatever you are driving with those shift registers will increase your current draw.  

I read a bit more on decoupling capacitors and it makes a lot more sense now.  I don't think I'm going to try to put them into this project, since it's a prototype, unless it becomes apparent that they're necessary.

When you are spreading your power across that many ICs and components, decoupling capacitors are extremely important.  Try and add caps anywhere you can to help your power distribution.  Next time you build a prototype, keep in mind that generally a 0.1uF for each IC is generally a good idea.  (And it is always easier to remove stuff later than to add it in.)

Would that make a difference with the ground, though?  The common +5V wire doesn't shut off the Arduino.

because the circuit isn't complete until ground is connected.

Are you powering everything off of the Arduino's regulator?  You might be overloading the regulator or whatever power supply you are using.

In the future, don't waste people's time with cross posting.

The other post:  http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1288477264

The USB ports work fine with other devices, there is some glitch in the Arduino ap.

Before blaming the Arduino App, it would probably be a good idea to check the USB Devices listed in System Profiler.  Make sure the OS is seeing (and recognizing) the Arduino board.

Are you powering the h-bridge with the regulator or directly from the battery?