I could easily be wrong, but I think your now-running Win 7 will generate a bootable repair CD. Not sure how to access that functionality. If it will, then start VL, insert the CD, and copy disc to ISO. That'll grab its bootsector and everything. When it's needed and you've lost the "original", just burn the ISO back to CD.
If I'm wrong about Win 7 making one, suppose you could ask to borrow the one you used just one more time to pull an ISO image. But I wonder: If Win 7's got enough left to say "insert repair CD", what are the chances that you could press F8 at boot and fiddle around 'til you get a Command Prompt for running chkdsk?