Allright now, this is important.
Because I tend to get carried away when i get into Zbrush, i usually unwrapp my model cleanly before detailing the model. That is because if you suddenly decide to continue on with painting maps after doing the displacement, having overlapping uv's will either crash Zbrush, or you will have to do and automatic unwrapp in Zbrush, in which case forget about editing anything in photoshop later on... There are two very cool peltmapping tools out there for XSI... Google it up, it's worth it.