I upgraded to Mac OS X Lion and I can't run the installed Windows anymore. It seems the issue is that the Lion installation created extra partitions so the Windows partition has a different number one. It's disk0s4 instead of disk0s3 (if I recall correctly).
Searching online found several discussions about it but only one with a proposed solution, https://discussions.apple.com/thread/3199099, essentially:
bootrec.exe /FixMbr bootrec.exe /FixBoot bootrec.exe /RebuildBcd
which didn't work. bootrec.exe /FixBoot claims that no windows partition has been found.