How to remove an old OS from an old drive you want to use

Hello Friends,

I recently built a new gaming system.  The OS is Windows 7.  I want to keep the WD hard drives from my old system because all my stuff is on them.  The problem that I’m having is that Windows XP is on the old C drive and it boots up instead of Windows 7 when it is connected to the IDE port. 

Here is my question;  Is it possible to turn off the XP on the old hard drive and still be able to access all of the files on it? 

can you change the boot priority of your drives in bios?

Thanks a lot.  That did the trick.

glad to help