1. We'll assume that at the moment the system can boot to the Win 7 OS Desktop and there are no error messages other than some indication of the boot drive virtually empty of any more usable disk-space. If that is NOT the case, so indicate.
Btw since my very first posting on this system it no longer will boot at all and in fact the bios shows no hard drive at all at this point for sata 1-4 shows none detected all of a sudden? If I can't save anything and at this point not sure I can will I be able to get them Windows 7 version they had by using what I see under Windows activation as the product ID?
2. Assuming no significant problem booting to the Desktop, can you (together with the users) delete as much unnecessary data from the drive at least for the moment in order to at gain a reasonable amount of additional available disk-space to gain some temporary "breathing room"?
2. It's a virtual certainty the system will support a 1 TB HDD; that's not a problem.
3. AFAIK the motherboard will NOT support memory > 4 GB, so check that out. In any event I seriously doubt whether the system could profitably utilize RAM > 4 GB. Again, if the users are engaged with only light-duty operations, e.g., accessing the net, email, and the like, 2 GB of memory should also suffice.
Something like this should more than suffice...https://www.amazon.com/PC2-5300-DESKTOP-Modules-240-pin--Tech/dp/B00C53DK3E/ref=sr_1_3?ie=UTF8&qid=1466547731&sr=8-3&keywords=2gb+5300+desktop+memory
(NOTE: I'M ASSUMING THE BOARD IS POPULATED WITH DDR2 MEMORY. CHECK THIS.)
4. IN THE MEANTIME, ENSURE THAT WHATEVER IMPORTANT FILES ARE CONTAINED ON THAT 80 GB DRIVE ARE COPIED TO WHATEVER MEDIA IS AVAILABLE TO THEM. THAT'S THE CRUCIAL THING AT THIS POINT BEFORE YOU GO ON. CAPICHE?