There are three parts to migrate...
1) The application itself, Parallels Desktop (PDM)
2) The application settings
3) The virtual machine(s) (Your XP)
#1 PDM will likely have to be reinstalled on the target mac, Migration Assistant will not transport all files necessary, it will have to be reactivated.
#2 Migration Assistant will likely transport this
#3 If this is not a bootcamp based Windows XP, the VMs are in ~/Documents/Parallels, MA will likely transport this also. If it's Bootcamp it's more complicate (MA will not transfer at all).