YK pointed out new hard drives are cheap: but
http://www.tomshardware.com/forum/27924-35-toshiba-satellite-hard-disk-replacement
points out newer or bigger drives are likely to run hotter, quite
probably exceeding the cooling capacity of the (year 2000) fan.
I doubt that, if anything newer hard drives would be more likely to run
cooler than the older ones. Besides, they've been designed to run under
some very unchanging maximum temperature conditions on laptops for years
now. Whereas desktops have soared in temperature, the laptops have had
to stay within the same temperature envelopes.
So I shall run Seagate or WD diagnostics in case they work . . .
Either is fine, and you don't have to limit yourself to them either.
There's plenty of good freeware and trialware utils out there, such Hard
Disk Sentinel or HD Scan. Both will read the SMART data off of your hard
drive and report it back to you. HDSentinel actually has a great
summarized rating system.
Yousuf Khan