Your graphics card should be fine if you're not a serious gamer, and fine for FM2012. The weak link in your system is your CPU so you're looking at a motherboard / CPU / RAM replacement at a minimum.
Personally I'd be looking at a SandyBridge i3, or i5 if your budget stretches far enough. You can buy 8GB DDR3 RAM for £30 here. A motherboard such as this should do the job. If you plan to keep your current hard drive and DVD drive then check they have SATA connections, because if they have the old IDE connections (ribbon cables) you'll either need to replace them too or find a motherboard with an IDE socket (one IDE socket supports 2 devices).
Hope that helps get you started.