You really need an entirely new system if you plan on running any modern titles. The Pentium 4 CPUs all fall below the minimum system requirements for most games these days, dual core is the minimum, and quad core is recommended on most titles. As said above you can throw in another gigabyte of RAM and a 9800GT and that would offer okay performance in games that don't need a dual core, though the vast majority of these are from 2007 and earlier.