what brand? how many amps on the +12v rail?
depending on psu, (from less costly to the more)
radeon hd 5670/6670 1 gb gddr5 ,
5750/6750 1gb gddr5,
5770/6770 1gb gddr5,
6850 would be the best for that res. it would cost the most, though.
My 5770 runs BF3 on high pretty well(1080p)... around 35-45 FPS... playable. May want a 6870 just to be sure... also, your 450w PSU is pretty weak... it would be better to get a bigger PSU, but it may run the 5770 fine. I have a 600w for my 5770.
how many amperes on the +12v rail?
look at the side of the psu, there should be a ratings chart. find out what does it say under +12v or if the psu has more than one +12v rails e.g. +12v1 and +12v2 or +12va or +12vb or so on.
if it doesn't have enough amps, upgrade the psu and you could fit more powerful cards.
i mean the Ampere numbers - usually denoted by A , unit for electrical current. usually it says something like '+12v - 20A' or has 20A printed under +12v.
what does yours say? can you post a photo of the ratings chart/ link to the exact psu model/ state the exact brand and model number of the psu?
damn... it's hard to figure out what's written under the +12v rail.. i think it says 14A. could be 18A. you're better off looking inside your case and see what's written under the 'yellow' '+12v' column.
anyway, your psu seems quite underpowered. it could use an upgrade if you want to install a new gfx card for playing latest games.
imo, get a 500-550W 80+ rated psu - you can use a radeon hd 6770 or 6850 in your pc, with your current psu - none.