The Windows 7 install DVD has a "Repair my Computer" console with the same tools as on the Repair Disk, including Startup Repair which will repair or rewrite the boot files for Windows 7.
But since Startup Repair runs many tests, it will assume that a fix it provides will also boot the OS, which isn't always the case if more than one fix is needed. So it needs to be repeated sometimes up to 3 times, which usually means it has finally decided to rewrite the MBR since all other fixes have failed.
However, just running Startup Repair for Windows 7 will not reconfigure a dual boot, so you need to go on to running a repair install from the Win7 desktop (now that you're in) which resintalls the OS (upgrade over itself) and reconfigures the boot.
There are more technical ways to achieve this but this is the automated way.