Possible to purchase notebook parts?

[Zap]

I have a Dell Latitude D800 that was a special deal - but was lowest end at the time (Dell gives good base deals but charges too much for upgrades). So far I've upped the RAM and have ordered a mini-PCI wireless card. Dell has instructions on how to remove the CPU (Pentium-M 1.3) and the video module (Geforce4 4200 Go, 32MB). I was wondering if it were possible to buy better replacements. I've seen mobile P4 chips in retail boxes, but haven't seen Pentium-M chips. Also, I've never seen mobile video cards for sale. Anyone? I know the Pentium-M is available up to 1.7GHz and the video was available as a 64MB module.