I'm not an expert on this, however I would say that to be "Legal" you will need to purchase a Mac and either triple boot (bootcamp) or use VM's to run XP and Linux. I would think that the iTunes and iTouch will work in OS X, as they're parts of an Apple product. Also you may have to consider getting Windows 7 unless you can find a copy of XP (or get your current one actvated on the new PC).

Have a great day
Patrick.