battlefield 3 on pc will it run it?

The 5450 is not a gaming card. That computer will struggle to get playable framerates on BF3. You need to bump up the graphics card to at least like... A 5670 at the absolute minimum, but even then you want to look more at something newer, like a 6770 or a 6870 if you have more money to spend.

BF3 really needs a more modern, powerful graphics card. The processor is a bit weak as well though, so you probably want to look into moving up to one of the newer Sandy Bridge processors or something. The i5-2500K is a good starting point that's not terribly expensive and will give you a lot of bang for your buck.

you definitly wnat a quad core if you got the money i suggest intel i7 extreme i use this and with bf3 its a beast my computer has never lagged even though i am live streaming at the same time its so awesome. make shure you have a really good cooling system or just go up to a 8 core so you dont have such a load on only 4 cores. my friend has one of these and i have never played on somthing so flippin awesome. still if you want to go super pro get a 12 core.