Getting a quad core may or may not be necessary;
http://www.tomshardware.com/reviews/...-cpu,2280.html
This article shows that back in 2009 no games made use of over 2 cores in a CPU, or at-least not much use, you're looking at a future investment if you're thinking of buying a quad core, as it won't improve performance much today. That doesn't mean however you shouldn't replace your CPU, as a pentium just isn't that fast compared to any modern CPU. If you go intel get a cheap core i3, i3 2xxx or i5 2xxx plus a sandy bridge (LGA 1155) compatible motherboard, if you go AM3 instead then just pick your self up any phenom processor and an AM3 motherboard.
Various options around $150: (Don't forget you'd need a new motherboard on top of this) (Prices approximated)
LGA 1156: i3 540 ($110) (2 cores)
LGA 1156: i5 760 ($200) (4 cores)
LGA 1155: i3 2100 ($120) (2 cores)
LGA 1155: i5 2300 ($176) (4 cores)
AM3: Phenom II x4 840 ($110) (4 cores)
To compare these CPU's and more check out Tom's Hardware's charts:
http://www.tomshardware.com/charts/d...aded,2407.html
As for GPU personally I always go with an x60, a 460 is a powerful card, you shouldn't need anything more than that unless you have a big screen or somehow really -need- to play metro 2033 at highest settings. A 560 Ti would be my personal choice however, as it's more up-to-date and has really shone in the GPU market. The 560 retails for around $230.
Lastly for PSU you don't need more than 450 watts for a 460, they only use 160 watts at load.
http://www.bit-tech.net/hardware/gra...card-review/11