Want to Upgrade my Graphics Card

The best in my opinion is the 7870. The gtx 660 is also decent if you prefer nvidia products.
The problem is that your cpu is probably a significant limiting factor. It would be helpful if you could give us better information on the exact cpu in your system, along with the other components (RAM, PSU wattage, etc.) and also if you could measure the dimensions for graphics cards fitting into your case as it appears to be quite a tight fit for modern cards. Primarily length.
Because your cpu is probably a significant limiting factor I wouldn't be surprised if a 7770 is your best option. Also you may need a better power supply to run the new graphics card.

Okay my specs are:
Intel Core 2 Duo 2.2 Ghz
2.0 Gig Ram
Windows 7
It's basically this one:
http://www.dell.com/us/dfb/p/vostro-200/pd

7750

Yeah unless you also upgrade the power supply to like a 450w unit you'll be stuck with the 7750, and even if you go up to the 7770 or 7850 the core 2 duo at 2.2 ghz is going to be severely limiting your framerate making the extra expense meaningless. I'd try a 7750 and see if it works without a psu upgrade.
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I don't think being "stuck" with the HD 7750 is such a big deal... It's still around 10 times better than the pathetic onboard graphics. And unless you plan on playing some seriously demanding games (2011, 2012 shooters) you'll be all right, even at 1080p.

It is also the best bang for the buck right now, too.

I found out my PSU is actually 160W. What power source do I have to get that would work with the graphics card and what video card could fit, because the mini tower doesn't have to much space?

No way - are you sure it's not the slim-tower version? If so, you might be better off getting a new computer. I'm sure you can find an i3 minitower for around $300 this weekend. Buy an HD 7770 to go with it.

You have 2 options. You can buy a new case and power supply, put the old system in the new case, and add a graphics card, or you can buy a new computer.

I'll just look at the sales this weekend I guess, if I can't find anything good, I'll reply again   Thanks guys