Uncle's old Emachines (lol)

well i finally talked my uncle into upgrading his computer- firefox is way slow when my computers needing repairs!!- so i found the systems max memory (512) and installed it, works quite a bit faster, but the system seems to freeze every once in a while, im not sure if its to do with the memory, or just the SITES he goes on.... if ya got me there... usually the screen just freezes, (firefox has crashed once during this post) but sometimes there's a graphical error, everything appears glitchy..

the system is an Emachines t1440

Any help would be greatly appreciated!

I googled Emachines t1440 it it shows 1.4ghz Celeron....

My advice for machines this old is that there are tons of 2-3 year old systems out there that are dirt cheap... I have bought tons of Dell Optiplex systems, 320, gx620, 745's.. go look on ebay. Lot's of sellers out there have tons of these for low prices. I got a Gx620 ultra small for $80 last week w\ a 2.8pentium d, 512,80gb, xp pro.