From a linux command prompt, and as root, type lilo -u <enter>.
If that gives an error about the time-stamps not matching, try lilo -U <enter> (note: that's a capital U this time!) Don't worry about the warnings, its never failed me yet!
As an aside, and just in case you do have to do a more fundamental repair, note that windows 7 uses TWO primary partitions, and its the smaller one you need to boot to get win7 going again in the unlikely event of anything going wrong. Its NOT the windows partition you need to boot!