If you have a PC with a Pentium forget about buying "more" ram, just upgrade the whole thing. And specs would be nice (hint: google Speccy).
It would be nice to know your budget too, nowadays you can get a decent Sandy Bridge-powered PC (coupled with a "casual gaming" gpu it would be "perfect" for every normal person) for around 700-ish I think, if you're willing to buy something lower end, an AMD gaming build with a "casual gaming" card would come even less.
Sandy Bridge build I would get for a normal user / gamer in my crappy country (note that if you live in the US you'll get stuff cheaper and if you live in a "normal" country like Germany, UK... you'll get stuff cheaper too):
Random ATX case with flashy colours: 40€
Random 700W PSU: 50€
Mobo - GA-PH67-UD3*: 90€
CPU - Intel 2500**: 200€
CPU cooler - keep the stock one**
RAM - 4x2GB random 1333MHz ram***: 100€
GFX - Ati 5770 ("decent" gaming): 120€
HDD: 2x500GB****: 80€
DVD - any random: 20€
*I don't even buy anything other than GA for normal PCs nowadays, they're simply the best. Enjoy USB3 and Sata 3
**Get the unlocked 2500K and something like the Mega Shadow and decent fans if you want to OC, but I doubt you're an OC enthusiast
***Don't worry about latencies and stuff, just get the normal stuff, once again, I doubt you're an enthusiast
****Hardware raid0, any 2 normal disks should work ok, if you want to save money and don't really care about performance just buy 1 disk