Answer to "Can I tether my iPhone to my iPad?"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.
Answer to "How to install 2009 logic board into early 2008 mbp?"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.
Answer to "How can I get my music back?"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.) :(