Naturally everyone here is familiar with such p2p sharing programs as kazaa lite and grokster.
Question is - since one normally leaves them on and downloading for hours at a time, does this cause excessive hard disk wear and tear in the long term. I listen to it and it's like "hrmm hrmm rhmm rhmm" writing tiny little packets over and over as it downloads. Surely over time this is a real strain on the old hdd? I have one hdd that I think died this way. Anyone else have similar suspicions?

Yes, my HDD's facing the similar stuff sounding like that.

Moreover, I'm becoming more and more suspicious about the one partion's space,
which I'm afraid is being slowely but surely eaten up somewhat.
I mean I didn't install so many progs so that the space could so quickly shrick from 4.4 Gb to 1.6 Gb,
despite the fact that I very frequently use cleaning stuff like Norton Fast & Save Cleanup,
System Mechanic and RegCleaner

most older hdds make some noises when writing and reading but thats normal and if you are afraid your drive will die from use of kazaa i think you should be more afraid of windows virtual memory.

I don't have an exact date ad it probably differs between models and manufacturers but i'd say 2 years and older maybe my 4 year old hd sounds like a chainsaw and it always has but my new one from september I can barely hear. Generally I'd say that if the drive has always been making noise it's nothing wrong with it but i'd get suspicious if it started to make more noise than the usual. And just to be on the safe. Make a backup of your important files.