I've been running Access 2000 -- admittedly installed as part of Office 2000 -- on both an XP Home and an XP Pro machine without having to install any of the service packs. I could easily be mistaken, but I believe those all have to do with flaws in how earlier operating systems (Windows 2000 or Win98SE) dealt with the software. My XPPro machine is fairly new, but the other one is three years old (at least).
My old (recently deceased) desktop had Win2K on it, and the Windows update process always found any updates for Office 2000 -- but the XP update system has never done so.
Frankly, I'd try installing your order manager program and see if it works. I'm betting you won't have any issues.
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