Need help finding a compatible sized graphics card

Hello everyone,

Im currently using a Gateway Dx4850-27e with built in intel graphics. The performance is okay but its just not enough to play games like tropico 4 and civilization 5 on high settings. Im connected to an 47 inch HDTV capable at 1920x1080 resolution through hdmi. I'm looking to get a graphics card that will help me play the above mentioned games at high settings(and possibly the new simcity game). No need for super high end cards as I usually stick to casual strategy games. My power supply is a wimpy 300 watts so I'm looking at getting a cooler master 600w. It comes in a package with a evga gtx 550 ti for $216 on newegg with a $40 mail in rebate. The card is 8.25"x4.38". I opened up my case but I don't know if it will fit. There's this little heat sync located not too far from the slot and it looks like it would get in the way. I took pictures but I can't find a way to post them on here. If there are any other suggestible cards and or graphics cards, I'm all ears. Thank you.