Will my gpu bottleneck my cpu?

Yes. But I would also not recommend a dual core CPU for gaming. The Athlon IIx3 440 is a better choice with 3 cores and a high clockspeed at a lower price. More games today can take advantage of multiple cores than ever. 3 cores is the average "sweet spot" for budget gaming.
The graphics card should be your main concern in gaming. I'd say on average you should spend twice as much on the graphics card as on the CPU to get the best gaming performance for your money. Depending on your current CPU, you might even be better off keeping your current one and spending all your money on a new video card.

You do not provide enough details for us to fully help you. We need details on your system, your situation, funds available etc in order to better help you. That is, if you want help beyond your question.

Also, ideally you will want 4GB of ram total. I struggle with 2GB with my quad core athlon and radeon 3870 but it is still acceptable for most games at the settings the 3870 can play smoothly at.

i would get an athlon II x3 435, OC it. Newegg has a ATI 4850 for $80 after rebate

total cost would be almost the same as a phenom II x4 955

ok thanks guys-here's more info as I need more help for sure.

my current system is the following:
3.0 ghz pentium 4 processor
some cheap asus mobo (Pg5mx . . . )-NOT compatible with ddr3 ram
nvidia geforce 7950gt 512mb
2gb kingston ram (ddr2)
windows xp sp2

Can't give any more details as don't have pc at my current residence. My budget is 500 at the most. But, it's really 400, as I'm definitely getting a new 500gb hard drive, which will cost around 100 i think. As for ram, well i guess thats another thing i could get if i got a cheaper cpu . . . I want to get the best long term gaming value/performance out of an upgrade as possible.
But, some other important things-I dont' want/need 'the best' gpu and cpu you can buy for gaming- just being able to play games like cod4 and assassins creed at high graphics and 1600x1050 resolution would make me very very happy!
1 more thing-I don't think overclocking is an option for me-I know nothing about it and I don't want to risk it, so don't consider that.
Any further suggestions would be great!

I can't find the video card deal CT is talking about but here's what I recommend for that money:

radeon 4850 XFX
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Athlon IIx3 440 (or the 435 if you want to save $6)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Asus motherboard
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Memory:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Should come to <$400

$95 ATI 4850 ($80 after the rebate)
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

$80-85 for the Athlon x3 435-440