The major difference between Windows XP Pro and Home for Mac users depends on which Mac you have. If you have a Mac with dual processors and dual cores you want the Pro version since it supports all four cores. The home version does not. So, if you have a Mac Pro, you really should get the Pro version.
The OEM version is just as good as the full retail version. Just make sure that you get the OEM version that already includes SP2.
balamw and I disagree on on whether you can move XP OEM to a different computer or not. In fact, I just did that and had to call MS to get a new authorization number. I reported to the MS operator that I was moving an OEM version to a new computer and all he asked was "Will this copy be loaded on more then one computer at a time." I told him no and he provided me with a new authoriztaion number with no problems. In any event, you can not have the same version of XP OEM on two computers at the same time, and that includes even loading the OEM version of two different partitions of the same computer so I have been told. So if you are operating Parallels Desktop and also BootCamp you should have two copies of XP OEM. I have not tried to have both loaded at the same time so I don't know if MS is actually inforcing this.
Dave