Very minimal flash and ram. The code is embarrassingly simple. In terms of pins I will need one in and one out plus ground and power I suppose.
You might get away with the Tiny45, or less. They're cheaper.
Your end product should use surface mount and I gotta warn you, that's not beginner easy to use. There are people here who do that stuff and might save you in time alone more than the cost, so check around about that. Just before you "go to board" make real sure you have a good, solid circuit which you can use a larger DIP chip to prove out. Don't rush it, be sure before you carve in stone.
I think that Frank Zhao may still be a member here, and he's not the only one that can do things like this USB business card (check the size of the Tiny and parts on that!):http://hackaday.com/2010/10/29/tiny-usb-business-card/
OTOH you might find something already out from China that you can reprogram and use.
Speaking of which, how do I run power into the ATtiny?
About 3/4 the way down on the MIT page shows pinouts. The 45 and 85 power pin is on the upper right when the notched end is up. http://hlt.media.mit.edu/?p=1695
The 45 and 85 power pin is on the upper right when the notched end is up. You will be using a battery I am sure, start checking into disk batteries and rechargeable li-ion types used in small MP3 players. You should not need a regulator except on a charger. Pick the right charger for price and voltage or go with cheap (in the short run) eco-bad disposables.
Sorry for all of the beginner questions. A book is on order so I'll be asking fewer questions soon.
Book is nice to have but for just this project you didn't really need it... but it may help. What you also want is the datasheet and maybe an application note from the ATMEL site. ATMEL makes the chips and do have a lot of free support. The hard part is finding just the stuff you want, they make a lot of different chips!
ATtiny's. This page will help you pick and choose, for sure.http://www.atmel.com/products/microcontrollers/avr/tinyAVR.aspx
Sometimes you will have to dig at bit.