FC2, Win XP and two harddisks

[Thomas Korsgaard]

Hello List

I have a computer with two disks hda and hdb. I currently have Win XP
installed on hda and FC2 on hdb. Now the thing is that I don't use my
Win XP any more and I keep getting messages that the disk is full. So my
question is: 
How do I convert my hda so I can use it under Linux? Is there a simpel
way of formatting it and then mounting it at /mnt after wards?

Thanks
/Thomas