well first of all i think you meant that u are using WIN7 (not win6) . But that is not the point here.
If you are not sure what exactly you are doing you should definitely backup your data. Next, i will describe my situation - i was running BT4, win7, slack - i burned bt5, booted from it, in instalator i simply deleted bt4 partition (its done by gparted if I am not mistaken), on the free (old bt4) space i created more suitable layout for me, and installed BT5 here. WIN7 and Slack survived with no harm and all 3 systems are booting just fine. BUT again, if you are not completely sure what are you doing, always (ALWAYS) backup your data first - btw. why to backup partitions?win7 fresh install is piece of cake (same goes for BT5 - great job dev team).