1 Open a terminal (Applications -> Accessories -> Terminal)
  2 In the terminal type "sudo gparted" without the quotes
  3 In GParted, click on your Windows partition.
  4 Choose "Resize"
  5 Make it the size you want it to be
  6 Hit OK or Apply
  7 Click on the unallocated space
  8 Click "New"
  9 Make this partition's size be 1 or 2 times the amount of RAM you have.  This is for your swap (pagefile)
 10 Click OK
 11 Click the rest of the unallocated space
 12 Click "New"
 13 Choose ext3 for the filesystem
 14 Click Apply
 15 Start the Installer
 16 When you reach the part about partitioning, choose "manual partition"
 17 Click on the partition that corresponds to your memory size (the swap one)
 18 Click the edit button
 19 Mark it to be used as swap
 20 Click OK
 21 Click the other partition
 22 Click edit
 23 Mark it to be used as ext3
 24 Make it's mount point just a / (it's a choice in the drop-down menu)
 25 Click OK
 26 Click the checkbox on the line which is mounted as / if the checkbox isn't checked
 27 Click the "Next" "Forward" or "OK" button to move on