SSD hard drive v the traditional one

Hi, can someone point me to a guide where I can read up about SATA HD's please?
I've had so many probs with my PC (just keeps freezing) that i've started to come round to the idea of just getting a new (refurbed) one, like this:
http://www.ebay.co.uk/itm/FAST-POWE...t=UK_Computing_DesktopPCs&hash=item20d02f88fb
For £99 delivered it seems that it'll be cheaper than taking it (my existing PC) to have someone look at it.
But I don't understand the terminology of a 80 gig hard drive? It seems too small? My current HD is 287 gig capacity with 185 used and 102 spare (as taken from properties)(don't know what the manufacturers description of size is).

I've run all of the malware and registry and cc cleaner type progs in an attempt to fix my PC. Auto defrag running. memory checked and ok, HD checked and ok. no trojans or anything. People say it's this (driver) or maybe that (processor) and that you should run this/that/other to check it... but when the PC is frozen and in full blown 'computer says no' mode it's difficult not to do anything except contemplate smashing it to pieces :-D

Help please :grouphug thanks in advance