HDD Formatting Question

[wolf2009]

I have two OS installed on two different drives. One drive has Vista, other has Win 7.

Can I go into Vista and format the Win 7 drive without causing any trouble ?

[Stoly]

sure no problem

I'd use disk management or diskpart to delete all partitions first, then create a new one and format.

[MrF]

It depends on your definition of "trouble".
Your boot menu will keep coming up at startup. You will need a startup repair to remove it.