Hey, I just looked up you MoBo specs - apparently it takes Core2 CPUs. I would recommend getting a new CPU as well - I don't know your budget but I would look into the E7xxx and E8xxx series - those will give you some serious gaming oomph over your current P4, and you may even consider getting a better graphics card like 9800GTX+/9800GX2 (those cards do exist, right?), if you can get them cheap enough, they can pretty much max out Crysis, and if you're willing to go ATI the Radeon 4850/4870 would be great choices as well.
If you're on tight budget, something like Intel E7200 and 8800/9600 cards with a new PSU would be something you could consider.