Just as a reminder, the 3G radio in the iPad only works with AT&T's network in the US. T-Mobile SIMs can be trimmed and used for data, but you will only get (very slow) EDGE-network speeds.
You will have much, much, MUCH more success at this endeavor by doing the following: Sell your 2008 MacBook Buy a used 2009 MacBook The net difference in cost will be much less than buying a motherboard for a 2009 model, then likely destroying it by trying to fit it into a chassis it wasn't designed for and interfacing it with components that are incompatible. Even if you don't destroy the new motherboard, you'll need to resell it and reassemble your 2008 again anyway. These are two completely different models with different cooling systems, display components, etc. People are telling you it can't be done because they're trying to save you time and money. Take their advice, and trust the experts. I've modded many things, but this is one project that even I would not touch.
It has 512MB of SDRAM memory, unknown (at this time) speed. It's not anything like a netbook or laptop; the memory is not on a replaceable module or upgradable.
Re-rip your CDs into iTunes. Then you can re-sync to the iPod. (In the "being proper and legal" department, if you don't own the CD anymore, you can't keep the music anyway.) :(
There are two additional brass screws holding the top panel plastic on to the frame. They are 00 Philips and shorter than the ones securing the motherboard.