///Nods with Terrance///
Most motherboards in the Pentium classic (P-54), PentiumMMX (P-55C), and early Pentium II days had a BIOS limitation of seeing drives up to 8.4 gigs. Now yours being newer than that, seeing your AMD at 500....well, some boards hung around for a while with those early BIOS.
Ruling out that the HD is bad (by perhaps checking to see if another computer sees it), you can fix this several ways.
First...is to check documentation on your motherboard...manual/website/calling their suppot, and see what it's limits are. Often you can find a BIOS upgrade which will increase it's HD capacity recognition. This is the preferred method.
An alternative is to use something called "Drive Overlays". What they are, is a software package made by the hard drive manufacturers which work with early BIOS and their limitations...."fooling the BIOS" into thinking that the BIG hard drive is actually a little hard drive within the limits of the early BIOS. But drive overlays can get buggy, limit the performance of your HD...and create problems down the road sometimes, such as preventing you from "ghosting your image", etc.
Here's a quick article:
http://www.pcguide.com/ref/hdd/bios/overDDO-c.html
The new HD that you got...try calling support for it...they can be helpful. Assuming you're familiar with jumper settings (Master, Slave, Cable Select) Generally, most motherboards will take your single hard drive on primary IDE as Cable Select, if it's the only device on your primary IDE ribbon cable. Some motherboards don't like Cable Select (CS), but will work with Master. If you have two devices on the same ribbon cable, then you MUST have a master and a slave. Your primary bootable hard drive with the active partition will be master. cd-rom, zip, or second drive will be slave.
Sometimes looking for the CMOS reset switch can help things alonge too.....to totally reset your BIOS and let auto-detect do it's thing. Are your IDE controllers set to "auto" on all?
Hope this is enough to get you started. I'll be off for the rest of the night, gotta get up early tomorrow in anticipation of a long day of mopping up this new W32.goner virus.