a pretty common question, try looking at this thread.
to make the partition usable tho, you'll want to use fdisk to change the partition type to linux standard or whatever fdisk calls it (type 83 i think) and then format it:
mke2fs -j /dev/hda1
this will make an ext3 journaling file system, omit the -j to just make a normal ext2 system. then just add relevant entries to /etc/fstab