Windows XP upgrade???

not an expert, but I believe that since microsoft dropped 2000 so quickly and moved to xp, you probably won't find a 2000 specific upgrade. the box most likely only says 95/98/ME, because 2000 was there and gone so quick and they even dropped support for the OS. I think your upgrade will work fine, and as stated, give it a try, since it's already open. I would just do a basic upgrade first, and not reformat. this is because it will reformat, and then ask for your existing disk. and IF it won't accept your 2000 disk, then you'd be WAAAY up a creek. if it does accept the disk and finishes the upgrade, you can revert back, then re-install with a reformat and have a squeaky-clean fresh XP.

However.....any and all programs will need the install disk to put back on the computer. i found this out the hard way. i had just gotten into them when i did the xp upgrade, and wiped the hard drive. then i had none of the programs my puter came with, like office and stuff. also, when it did ask for the existing disk, the only disk Compaq includes is a "restore" disk, and it won't work as proof of existing OS. and Compaq wouldn't help me with that problem.
but....lesson learned.

never going to use Compaq again.

Also....microsoft is very helpful with these sorts of problems. when it came time to reformat again, i didn't want to buy windows 98 again to try to return it (i did that the first time and luckily was able to return it and get my $300 back), so i send microsoft a (free) tech help request, and they sent me a NEW INSTALL disk. no questions asked.

you could do the same and see what they recommend. they might tell you that 2000 is not serviceable, and send you a fresh install disk for xp.