You can play it. Of course everything depends on your expectations.
I played Crysis with my X1900XT 512MB in Windows XP @ 1920 x 1200 using medium graphic settings. I don't run in and simply start shooting. I generally play FPS games with some stealth. I don't recall getting annoyed about low frame rates until the final battle scene. I could tell I was getting frame rates in the teens.
I finally replaced my X1900XT with a HD 5850 back in Sept. 2009. Haven't played Crysis with my HD 5850, I got better things to do.
What! You are not going to try and get us to believe you have a life or something are you?