I'm in the process of designing an in car pc.... it will do the following

-read from accelerometers to do 1/4 times, estimate hp, etc.
-read from o2 sensors...graph...record and spit out info
-use a ready made 12v powersupply and power on protection circuit
-play DVD's...not really a big deal but something has to be bling
-run mdk
-no gps...no gps...but maps and directions, yes

This project will be similar to the other onboard pc projects people have made in the past except it will have a performance focus and not a ICE focus.

My major question to you all is: where can i find some good accelerometers, temp sensors (that can withstand high exhaust temps), etc. that will interface with a pc?

Depends on where you live. I know a store here in Amsterdam..........