re: Is it safe to use of XP via Parallels on a MBP?
A virus within Parallels should not affect your Mac. But within the XP environment I would recommend running some sort of antivirus program, probably a free one like Microsoft Security Essentials, Avast, etc.
Also I would suggest getting the Parallels VM set up like you want it with the antivirus and whatever programs you are using and then make a copy or clone of the VM. That way if the one you are using gets infected you can just delete it (assuming you copy your data somewhere safe) and use the copy.
Also I don't know what version of Win7 you have, but I believe the Win7 Pro version has a builtin XP mode which basically creates an XP VM within Windows. So you might be able to create a Win7 Parallels VM and then use that to run XP emulation mode just for programs that only work in XP.