Re: Drive format question.
I'm not 100% sure about Vista / Win7 with the new boot manager, but if you did that you might delete the boot files causing neither one to work.
I think if you're loaded into windows 7 what you can do is delete the Vista partition, then extend your windows 7 partition. Once that is complete you'll need to reboot the system and boot from your Windows 7 disc. Then you'll run a boot repair to reload the boot manager. (Not sure what it's called) Then you should be able to boot back into windows 7.
The main thing is that you'll need to have the Windows 7 dvd handy to get rid of the Vista partition. If you do then you should be okay, just make sure to backup data before attempting to extend the partition.