Those system specs are fine for most users. Not a great gaming machine or workhorse, but for surfing and general use, it's fine.
Have you inspected the system for overheating issues? Any fans recently start making excess noise, or, if you open the case and look inside without touching anything, are all the fans running? If there excessive dust in the case? Get a can of compressed air (~$12 from BestBuy or similar stores, cheap online) and blow all the dust, dirt and junk out of the case)
The other major reason for system lockups is software issues, thus...
Download, update and scan with Ad-aware http://www.lavasoftusa.com
and Spybot http://www.security.kolla.de
(did you update Spybot first?)
Then download a scan with Hijack This
Don't delete anything that Hijack lists, most are required files and settings, however, someone here can look over the logs for anything that could be causing the freezes.