Well, it would be a decent upgrade, and it does appear to have good ratings, aside from the fact that it's only rated by 2 people at this point in time.
Does your previous card have a fan? I've noticed that frequently on cards with heatsinks it's very important that your case has good airflow, as the lack of a fan on modern GPUs can generate good amounts of heat if there is not the proper air-flow in your case. This probably won't be a big issue though.
Aside from that, just make sure that everything is compatible, sometimes for upgrades like these may require more power from your PSU.
don't get 5750, for sure your cpu is already old.
Get sapphire 5570 , its $54 after mir in newegg. Its much better than a 5450.
Don't bottleneck your computer with that card. Get a lower price-based card that will work efficiently with your CPU.
I would not spend that much on one get a low priced one which will do great on your CPU
And just a side note, I have had bad experiences with CompUSA. I primarily deal with Newegg, with the on-occasion transaction with Tiger and have had good luck so far.