There are many items you didn't tell in your post. Such as what jumper setting you used, the cable type, why you didn't have Dell walk you through the BIOS update, what XP Service Pack is installed and most important if you followed Microsoft's instructions to set it to PIO, Ok your way out and then go set it back to DMA if available.
Why? Because it's broken. Read http://www.microsoft.com/whdc/device/storage/IDE-DMA.mspx and read CAREFULLY how Microsoft tells you to flip it to PIO then back. I repeat... it's busted.
Bob
I have a Dell Dimension 2400, running XP, with 512KB of memory and an 80 gig hard drive.
I added a second Hard Drive (160 gig) as the Slave on the Primary IDE Channel.
It works fine in every respect except speed -- which I discovered when trying to record and play back .avi files, which are badly fractured in both sound and vision.
Thanks to help elsewhere on these forums, I think I've identified the problem:
Although the Device is set to "Ultra DMA where possible" it sticks to PIO Mode. The other three devices (main hard drive and two cd-rom drives) are all operating in Ultra DMA mode with no problems.
I don't think there's anything more I can do through Device Manager, and it appears that BIOS is the next step. I'm way out of my depth there without any advice.....so I'd welcome some. Thanks.
FYI, here's the earlier post http://reviews.cnet.com/5208-6122-0.html?forumID=44&threadID=42259&messageID=495454

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic