I have a custom built PC

my case includes:

6800GT PNY Nvidia card

AMD athlon 64 processor 3500+ 2.20ghz

1.00gb RAM (2x 512 sticks)

and plenty of hardrive space

i built this case about 2 years ago and i know that it has been getting a little dated but i was just wondering what specs i should be able to run most new games that are coming out at (mostly concerned about crysis)

is it maybe time to upgrade? if so what is a good PCI express motherboard and nvidia card i could go with to upgrade just those parts? i dont have the money to throw down on a brand new PC

thanks