PS 3.04 loaded just fine on XP Pro Sp 1 for me. Unfortunately it would not run. Was getting "Not enough memory …" error. Looking through the forum I found my 768 meg of ram was too much and needed to pull 256 meg out. The program ran fine after that. A "Thank you" to the forum members for that.
As Robert L. indicates, the upgrade to PS/cs will need Tech support to install. Three to four minutes tops was all it took after the Tech verified my previous registration. It went very well for me and the Tech was very knowledgeable.
Hope this helps,
DS