Sharing between Boot Camp and VM has several issues.
XP systems can handle the technical problems of multiple boot configurations. That is not so much a problem.
The real problems extend from things like Windows Activation. Whenever you make such a "significant hardware change", MS will want you to re-activate Windows. You see, Windows will think that going from Boot Camp to Parallels is the same as a complete motherboard replacement.
I suspect that Microsoft will be the ones to bank on this, with Virtual PC for Mac that has a corporate-edition of XP, no Activation, and proprietary boot configuration scripting so that VPC will go with boot camp. Of course, that requires two things; the MBU to have half a brain, and, of course, a leadership that would let them develop such a product.
I don't think this is going to happen with Parallels, unless they chose to support pirated copies of Windows that lack product activation.
Edit: As for accessing an existing home folder on BC, you can do that currently with a drive share. That will work for file access, but since boot configuration has changed, you really can't link local folders due to the different environments.
Last edited: Apr 13, 2006