The partitioner will show a bar, illustrating the partitons on the harddrive. Do you have 2 hdd's or is it just one with a partition? In either case, drag the separator on the partitioner bar to change the size of a new partition for mint.
The mint install will auto detect any other OS like windows, and you will be able to select what OS to boot with the boot grub loader when your computer starts.
If you need more detailed instructions, just post here and say where your up to and we can give you a hand.
| Compaq Presario F500 | AMD Turion64 |