win7/vista have restore points let's say a checkpoint in time. It's mantained by a special service on win7/vista even in "recovery environment". So you can rollback in time system critical things like exe, dll, registry etc. At every well written installation, hotfixes, updates a restore point will be made and you can rollback by "system restore". check points contain the OLD information in case a block is overwrtitten.
But .... as you started winxp as well (also has this restore points but works totally different) and probably accessed the win7 partition the restore points are invalid and empty! Please don't assign a driveletter to the win7 partition (in winxp) and don't access it!
But you can in win7 show the installed updates and sort them by date. uninstall the last updates you think that made your dvd invisible
