Windows 2000 SP3 contains updates to the following:

ipp_0013.asp
ipp_0004.asp
ipp_0010.asp
page1.asp
ipp_util.inc

If you have customized these pages, back them up before installing SP3, and restore the backed up files after the SP3 install.

NOTE: If you have created other custom Internet Printing Active Server Pages, as a safety measure, I would back them up prior to the SP3 install.