You will have to reinstall the Windows applications from their installations disks while running Windows in Bootcamp. As for the data, you will have to transfer it to a intermediate medium, such as a flash drive and then move it to the new Windows Bootcamp partition.
HOWEVER: Mountain Lion's Bootcamp will NOT support Windows XP installation at all.
NOTE: I have the mid-2009 MacBook Pro and while it was still running Snow Leopard, I installed Windows XP into Bootcamp and then I installed Parallels 6 to also run Windows XP from the same Bootcamp partition (Parallels does not need to create a whole new Windows XP.pvm file with duplicates of the Windows XP files; saving quite a bit of hard drive space).
I note that after I upgraded to Lion, I am still able to both run: (1) Windows XP in Bootcamp and (2) Windows XP in Parallels, although I did upgrade to Parallels 7 during this transition, even though it may not have been necessary.
SO: If you can go back to Snow Leopard, you can create a Bootcamp partition that will survive the upgrade to Lion. I have NOT yet upgraded to Mountion Lion, so I cannot answer the question of whether it will continue to survive that upgrade as well (although I am both hopeful and expect that it will).
Also, my advice is to upgrade from Parallels 6 to 8: you will not only save the interim upgrade fee that you would have paid for Parallels 7, you also will have upgraded TWO levels of Mac OSX - from Snow Leopard 10.6 to Mountain Lion 10.8!
Lastly, with Parallels 8 you will also be able to create a Snow Leopard.pvm file (with Rosetta) and be able to run any old PowerPC software that you may have occassion to utilize. Full Snow Leopard installation instructions into Parallels here:
http://forums.macrumors.com/showthread.php?t=1365439
