You are referrring to the 100mb System Reserved partition?
You need to mark Windows 7 active, then recover the MBR into Windows 7.
Boot the Windows 7 DVD Repair console or Repair CD, click through to Recovery Tools list, select Command Line, type:
SELECT DISK # (Windows 7 HD)
SELECT PARTITION # (Windows 7 partition)
Now return to Recovery Tools list to run Startup Repair up to 3 separate time with reboots as it will first attempt to repair and then write the MBR to Windows 7 partition.
Note: If you want to recover the deleted space into Windows 7, use free Partition Wizard bootable CD, rightclick Windows 7>Resize Windows 7 to include 100mb space, mark Windows 7 active, Apply steps, then run Startup Repair as given above.