SCO

need it to be able to run Seagate STT8000A tape drive. Any suggestions where to go.

The junkyard. 5.0.5 will not run on a P4, so you will need to find something at least 10 years old. I have an Acer 9100 series server with 256K of memory and a Mylex DAC960 Raid controller. It will need new disks.
Is your only reason for needing the machine to read the tape?

pretty much. The current machine is 10 years old and has an old 3GL data base running my entire companies financial. Custom built and it works great. Affraid I will come in office one day and the box won't boot. I need a backup box but SCO 5.0.5 will not run on new machines. I current backup on a QIC 80 mini tape connected to floppy controller. The problem started when I tried to install another QIC 80 on the new machine. Now I know I spent the last week trying to install something that wouldn't ever work. Is SCO still available for upgrade and does the upgrade work on P4?

I standardized on Dell GX1 systems (full tower or desktop) several years ago knowing that they would probably be around forever in the used market. Also stocked up on adaptec 2940u controllers, 3com 905 nics, and digi 8e multiport cards to keep things going.

Current GX1 listings on ebay are from $40 to $135, working.

One issue you might have is mounting the tape drive. IIRC, the drive is mounted in a set of rails to fit a 5" slot with screws on the side. The GX1 secures drives by bottom mount with spacing for optical drives.

5.0.6 (with patches) and up will run on a P4. The problem is that Intel moved cpu thottling (to prevent overheating) from the bios to the operating system.
Upgrading to 5.0.7 is a no brainer.
Upgrading to 6.0.0 takes some effort, but the results are well worth it.
Consider acquiring Microlite Edge, and backing up to DVD.
HP provide drivers and support for some of their Proliant product line. Be sure to confirm that you have the right model and options.

Going with Dell GX1. Buying two systems and upgradeing to 5.0.7. Why change everything is working great as is. I'll buy another two in a year or so. Thanks for all your help.