I had issues with running certain programs that were only written in 64 bit, so I upgraded the processor to use those programs and increase the 2GB ram limit to 4GB.
I used the logic board replacement guide to get me most of the way there. The project mat helped a ton because there were a lot of specialty screws involved with this project. (iFixit should have a guide for upgrading the processor. This guy's post helped me fill in the gaps http://www.tekrevue.com/stayin-alive-upg...).
Once I got the new processor in and put the machine back together, it didn't boot (AHHH!). Well, I checked all the connections and didn't an issue, so I thought I might have gotten a bad CPU. I took the whole thing apart again and put the old one back in, booted it up, and it didn't start either! Then, I notice that the ram looked uneven. I gave it a little push and it popped in. I tried powering on, and it booted just fine. I realized that there was a step when disassembling where you used the RAM ejection levers to help pull the front bezel off. I pulled the levers the wrong way at first and apparently partially ejected one of the sticks.
Well, another tear down, CPU switch, and halfway reassemble later, it worked. I finished up, and then used a little programs to let my computer make use of the 64bit Core 2 Duo. Now to get more ram and make use of my 4GB limit. I'll remember to push it all the way in next time.
First, there is not an explicit guide for upgrading the processor. There should be because it's just a few extra steps and iFixit sells the thermal paste and cleaner. Most of the contents of the guides are copied anyways. (A bunch of people came over mid-upgrade, or i would have taken the time to take pictures myself).
Second, It's rated as difficult, but replacing a smartphone screen is monumentally more difficult than this. There are a lot of steps, but there is no soldering or anything. The worst part was that the tiny plugs were brittle from age. USE THE NYLON SPUDGERS. When I didn't, I tended to crack the edges of the plugs.