moving drives...
Boofhead,
The reason the drive _may_ not have been detected is that you may have to change some jumpers (== "switches" comprised of two little pins and a springy piece of metal in a plastic case, which is used to short them out to "jumper" them.) Each IDE interface can have two devices on it. The first device installed must be the master - if a second one is installed it must be the "slave".
If you have plugged your drive from the old computer onto a bus thet already has something on it it in your new one, then you will need to change the master/slave jumpers on one of the devices.
On some discs, finding the master/slave jumpers is realtively easy -- on others it canbe "challenging" to say the least. The drive vendors web site *should* help.
The easiest option, if you can do it, is to plug he disk into the bus that has the CDROM on it, as the master/slave jumpers are ofter much easier to deal with on CDs.
As always when mucking about with your PC, take sufficient backups, precautions, etc., before starting, in case the worst happens ;-)
HTH,
DS