Did you install the operating system, or is it a live version?
If it is a live version, you may have to mount the hard drives manually.
If you installed it, then one of the hard drive partitions is now a linux partition and that is why you are able to see it. But in my suse experience, when you install the os (instead of running with the live cd), the hard drives mount automatically.
To mount a hard drive, you need to know where the hard drive is located, which will require a few command line entries. Open the terminal or console.
Enter "su" for super user (gives you all access rights). then the password, if required.
Then create a folder that you can mount the hard drives to: mkdir /media/hda1
Enter "ls /dev". This will show you a whole bunch of attached hardware devices on the computer. Look for the hd files. hda would be the first hard drive device and hdb is the second, etc. You'll have to determine for yourself which drive you want to mount.
When you figured out the drive you want to mount, enter "mount /dev/hda1 /media/hda1"
You should then be able to access that drive.
-> su
-> //Enter Password:
->
-> mkdir /media/hda1
-> //folder created
->
-> ls /dev
-> //contents of /dev listed
->
-> mount /dev/hda1 /media/hda1
-> //Drive is mounted