If the partition is the one you're booting Windows from, you'll need a Windows CD and a copy of gParted (free). Boot your computer from gParted and expand the partition. When you restart you won't be able to boot into Windows, this is normal. Boot from your Windows disc and go to the recovery options and then Startup Repair.
If that doesn't work, then go to the recovery options, then the command prompt and enter these commands:
bootrec /fixMBR
bootrec /fixBoot
bootrec /rebuildBCD
After that your computer should start again.