Anyone experiencing problems with Odin recognising their phone, blame the crappy USB drivers. You may need to attach, and re-attach the phone once Odin has started.
Try re-booting the phone, and or your PC.
Failing that install the Kies software.
See
Download Kies Here
It comes with later USB drivers. Also ensure neither Kies or PC studio are running when you run Odin.
If you're running Windows7 you definately need kies.