Did you install the chipset drivers first, then the system software, and finally, the drivers for all those components?

Certainly did

If you are missing the disk for WinXP, that would be a problem, perhaps the eBay
vendor could supply you with that.

In Device Manager, I show four "system Boards" all from Microsoft and they
list "no drivers needed or installed" which would mean that they are part
of Operating System and repair's would come from WinXP CD.

On System Properties, I have "Hardware Profiles" on General Tab, I only
have two; Docked & UnDocked, but can copy or create different profiles
as needed.

For example I could create a "Profile" with modem and wireless (or whatever)
"Disabled in this profile" (selected in Device Manager).

As you know, the Drivers and Utility applications are better to get from
Dell Product Support Download. They do not supply Operating Systems and
you should have the CD/CD's for that. Microsoft will mail you (for free)
the "Service Pack Two" CD (which you should have also).

On the underside of your D800, there should be a sticker from Microsoft
that will have the 25 character code required to 'activate' your Operating
System. This code would allow you to use *any* WinXP CD to repair or
reinstall your OS. *Sticker will also list XP Pro or XP Home*

If the seller has removed this sticker, you would need to
purchase an Operating System.

PatK, if you're missing just one driver on teh D800 and it's marked Base System Device, it's probably the driver for the smart card reader.  It's probably on Dell Downloads, otherwise I think it's a Texas Instruments driver - anyway, if you search the forum it's been discussed many time before.