Thinkpad R40 - what is the Biggerst/Fastest HD I can use?

[vk60402]

Right now I have 20GB, which, after hidden partition is really close to 15GB, after all windows and drives and other IBM programs (not including Anti-Virus) are loaded, it leaves me with 10GB. After I load my Anti-virus, Adobe, MS Office, etc.. I'm at 7GB free.

One of the options (cheaper ones) is to get a USB harddrive. Btw, anyone knows of pretty cheap/fast/small external harddrive that may be used with a notebook (i.e. don't require 120V power supply?).

Another option, is to purchase internal, 80GB-100GB hardrive. But the tech support told me that they don't recommend 5400RPM or faster drives on R40 (2681-CU1 is my model), as they tend to be hotter/not designed for my system, so I'll have to use one at my own risk, possibly voiding the warranty.

Anyone uses fast hardrives with their R40's? What is the max size YOU know will work with R40?

Thanks,
Vlad