The Service Pack is the same for Home or Pro, and is available for download
HERE - be aware it is a 266MB file; even with broadband, downloading it will take a while, with a dialup connection it likely is impractical to attempt. The CD is available free of charge
HERE
I'm puzzled by your report that the install process called for a Service Pack CD - it is to be expected an upgrade install would request an install disc for the original operating system, the one being upgraded, or if you are attempting to load an original, pre-service pack version of Win XP on top of a version of XP which already has a service pack installed, you will get a "cannot proceed; newer version is already installed" sorta message, but other than trying to install an older version of XP over a newer one, for an upgrade to a pre-XP Windows version or a full clean install, a Windows XP install proceedure should care not a bit for service pack status.
Can you remember or reproduce the exact, verbatim message you received?