Battlefield 3 requires a quad core and at least a GTX 560.
The 460 has a graphics clock of 675Mhz the 560 does 810-950 according to the website.
Even having a 560 is not going to allow you to fully enjoy the game with everything on ultra and a 1920x1080 resolution.
The x3 450 is dated so even if you buy a new card, you still will experience poor fps.
Use this link to compare cards and cpus http://www.anandtech.com/bench/CPU/2
You can find good deals over at http://www.newegg.com/