From what I understand, SEGA Sports is supporting all systems. However, I am unsure if NFL2K2 will be out on the Gamecube or if they are just going to wait for 2K3.
If you have a PS2, I highly recommend picking up NFL2K2 for it. The games is very well done on the system and I like using the PS2 controller a lot more for this game.
Like Dean said, they will be supporting all platforms with the Sega Sports brand, but they aren't bringing all of the titles to the Gamecube this year for some reason. (maybe the lack of online plans on Nintendo's part at the time)
Maybe it is just me, but I didn't think the graphics in the PS2 version looked as clean as those did in the DC version of 2K1. Now when the camera is up close to the players the graphics have been much approved, but everything else looks very grainy (with an S-Video connection). Maybe the Xbox version will have a higher resolution. Gameplay wise it seems a lot different than older versions of the series, but it is growing on me.