You won't be able to mount the hard-disk directly. You want to mount the right partition on the hard disk instead.
If you only have one partition (an “unpartitioned” disk), or Windows is installed on the first partition, then you can use /dev/hda1 (or hdb1, hdc1 etc.) to select the partition to mount.
To mount a Windows partition, you will want to use one of the following filesystems:
vfat (FAT16, FAT32)
ntfs (NTFS, as used on Windows NT)
There's also a filesystem that adds Linux device information to a FAT filesystem (keeping it in a seperate file), but I forget the name of it off hand.