dual booting xp and windows 7 question

so i have windows xp installed and want to install windows 7 also.
my first question is how do i do this without it deleting everything on my harddrive?
and if i install windows 7 on a completely different hardrive than windows xp will this create any booting problems?
thanks in advance

 

http://forums.afterdawn.com/t.cfm/f-165/dual_booting_windows_xp_and_vista-785884/

AFAIK, same answer

 

one more question
will it format the harddrive im installing it on or just the partition?

 

You install to a partition on the hard drive.

If the hard drive has no partitions, you will be asked to define one.

If the hard drive has existing partitions, you will ask which partition to install to.