I have purchased a new Seagate 400GB Ultra ATA/100 internal HD and an Adaptec USB/Firewire enclosure. I have followed the installation directions to the letter.
Here's the problem: when I plug in the enclosure to my computer (by USB or Firewire), the computer thinks that it is a different drive (one with only 80GB of space). I can format it and partition it and use it satisfactorily, but I am limited to 80 GB. I have checked device manager and its properties, and everything refers to this other drive.
It makes no difference as to whether I have the jumper on Master, Slave or Cable Select.
Seagate's support speaks of many different capacity issues - usually refering to the Bios. But, they specify certain GBs and 80GB is not one of them. I don't think that this is the problem as my computer is not very old and is running XP with SP2.
Any suggestions?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic