Jon,
I agree with Mac the Knife. It sounds like they just gave you an old piece of PC-100 or 133 that they had laying around for some reason or another.
If you are going to run Win2k get youself either one 256Mb stick or a 512Mb stick of RAM. Your best bet with Win2k is one stick of 512Mb PC-133 and forget your old stick of RAM.
Here is a list of RAM by price from Dabs. Look at the Crucial RAM for £54.16:
RAM at Dabs.com
Take Care,
Richard