So you can boot into the second choice yes?
If so just download EasyBCD and remove the secondary Windows Boot Option. Then your computer should automatically boot into Windows 7.
Once you've done that, try to boot using your Windows DVD. If you can get into it, then use the Repair my Computer link to run the command FIXMBR or the command bootrec.exe /fixmbr. That should repair your master boot record.
If you still can't boot into the DVD, use something like Parition Table Doctor ($$) to fix your mbr from within Windows.