can i run nfs mostwanted 2012

A 5450 is a pretty slow card, if you have a normal case and a power supply of about 300 watts, for $60 or $70 you can get much better performance with your CPU and RAM. Get a Radeon 6670, it's low end gaming card but will be a lot faster than yours, and will match your CPU pretty well.
 
You won't be able to run the game with Windows XP. All the new Need For Speed games, including Most Wanted 2012 use the Frostbite engine which is DirectX 10 and 11 only. Windows XP only supports up to DirectX 9. You're going to need to upgrade to Windows Vista, 7, or 8 in order to play, and your Radeon HD 5450 probably won't handle the game well, if at all.
 


Good catch, having XP right away puts the system out of spec to run the game.

Miniumum specs: CPU: Core 2 Duo 2.4 GHZ or Althon X2 2.7 GHz
CPU Speed: Info
RAM: 2 GB
OS: Windows Vista (Service Pack 2) 32-Bit
Video Card: ATI RADEON 3870 or higher performance / NVIDIA GEFORCE 8800 GT or higher performance
Sound Card: Yes
Free Disk Space: 20 GB

So, you need Vista at leat (Windows 7 is MUCH better) and a faster video card.