Hi,
First of all games VARY in how much a CPU bottlenecks things, but you should see a definite benefit in most games.
I don't know the exact difference but they are EIGHT tiers apart:
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
RAM:
2GB is a little low but I'm guessing it's DDR2 which is a little expensive now and also you are on a budget. Some games will have issues with that so if you buy any new games research the requirements.
POWER SUPPLY:
You may need a new Power Supply. With an HD7750/70 the lowest I'd recommend is a quality 350W. If you can't handle any card, the Antec VP450 is a pretty good PSU for about $40. It has a single 6-pin graphics connector.
CARDS:
1) $50 (after MIR):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814131481
Might not be the BEST card but it's pretty cheap and if it fails you still have the Warranty. If your budget is really tight consider this. I would prefer a BETTER card though.
2) $85 (after MIR):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814102969
Reviews seem good.
3) $70 (after MIR):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127687
This is an HD7770.
4) $90 (after MIR):
http://www.newegg.com/Product/Product.aspx?Item=N82E16814202011
*This is an HD7770 which has really good customer reviews.
The difference in cost between most HD7770's and HD7750's is small so I recommend the HD7770 unless:
a) You want the $50 HD7750 as your budget is small, or
b) Your Power Supply can handle an HD7750 but NOT an HD7770.
Other:
a) The Sapphire HD7770 has an ADAPTER for your Power Supply (4-pin Molex to 6-pin I believe) however your PSU must still be capable of handling the load.
b) GAME.
If you didn't know, you get a free game from a list (downloadable). I strongly recommend one of the Dirt racing games as they should be less CPU-dependent than the other games.
WARNING:
avoid 2GB video cards if you have 32-bit Windows. You would lose a small amount of your 2GB of System RAM.
Summary:
- YES. You will see an improvement in most or all games.
- Power Supply.
- My recommended card is the $90 HD7770 from Sapphire (if your PSU can handle it).
- 1GB VRAM if 32-bit Windows (not 2GB).