You may or may not be able to boot into Windows, but try it and see. This sort of thing does happen from time to time, and it's Parallels' fault. The fix is usually to repair or redo the Boot Camp partition. You should be able to access that partition from OS X and copy your data and such, but you may have to rebuild the partition.
To "fix" the problem, boot from the Windows CD follow the instructions in
this link to start the Recovery Console-there's a link on that page to a list of all the Recovery Console commands and what they do. Using the console commands that fix the boot sector ("fixboot") and the master boot record ("fixmbr") should fix the problem.
If instead of the boot data, Parallels messed up important Windows OS files, you can do a "repair" installation per
these instructions. A repair installation does not delete your files or programs, but does repair and replace OS files as necessary.
If all else fails, be prepared to copy your files from the damaged partition and start over.