WOW, I think you've bumped enough times. Sheesh.
I have the GA-7VT600 1394. I use an 80GB Hitachi Deskstar 7K2502 SATA drive and I have an additional 40GB IDE drive. I use Windows XP Professional and I have the SATA drive as the primary drive (the one that has the OS on it). If yours uses the IDE drive primarily, and the OS was already installed, then you probably forgot the drivers. If you DID install them properly, then just simply format the drive and choose a drive letter. You definitely won't see it before you do that.
I have absolutely no idea why, aside from operator error, the HD would just simply disappear on that motherboard. You really should make sure that you have the IDE cable plugged in properly and I don't mean making sure it is snug. Make sure that you don't have it flipped around, because that can always happen by mistake. The next choice would be to go into the BIOS and hit Ctrl+F1 for advanced options in the BIOS. Make sure everything checks out, such as that the proper IDE and SATA selections are chosen. The next step would be to load the failsafe defaults to make sure it couldn't be a BIOS choice.
If nothing works, then I would suggest you email or call Giga-byte's technical support for help. It really sounds like either a bad HD (the IDE) or you may have not done something you should have done and now can't fix it. Good luck, but I don't think you can really find much help here now. If you could, they'd have responded by now.