If you have 2GB of RAM, I don't think you'd feel any difference between 100GB at 7200RPM and 250GB at 5400RPM. Their performance is very close. If you have smaller RAM, you would be able to see a little bit of difference because HDD will...
For regular ATA support, 100GB is the biggest HDD for 7200rpm.
Check the link:
For SATA there is a 200GB model, but I believe Ferrari 4005 is not supporting SATA.
Celeron M chips and Pentium M chips are very similar and the only difference is the cache memory size. I upgraded my TM2434 from Celeron M 380 to Pentium M 745 and have used for a month without any problem.
I doubt you can upgrade it to...