For Windows Vista:

1. On your desktop, right-click on "My Computer" and click on "Manage".
2. On the left hand side, under the "Storage" heading, click on "Disk Management".
3. Windows Vista will now show you a list of all your hard drives and the partitions on them (if any).
4. Assuming you don't have any other partitions on your hard drive, you want to shrink your current partition to make space for a second partition.
5. So right-click on the partition and click on "Shrink volume".
6. A small window now appears. Next to "Enter the amount of space to shrink in MB", type in the size you want the new partition to be. Seeing as Windows 7 will need at least 16 GB or so, I suggest that you make this size no less than 25 GB (25600 MB) to give it some room to breathe. Keep in mind that you will be able to access your other partition through Windows 7 RC too, so you don't need space for files on the partition that you're going to install Windows 7 RC on.
7. Click on "Shrink".
8. Your hard drive will now show an "Unallocated" area with your original partition being smaller than it was before.
9. You now need to format this "Unallocated" area — simply right-click with your mouse on that part of the partition and click on "Format".
10. A "New Simple Volume Wizard" pops up.
11. Select a drive letter and click "Next".
12. On the next screen, select "Format this volume with the following settings", and then select "NTFS" next to "File system", "Default" next to "Allocation unit size", and give your new partition a name in the field next to "Volume label". Finally, tick the box next to "Perform a quick format".
13. Click on "Next".
14. Confirm the settings and click on "Finish". Your computer will now seem to have two hard drives instead of just one. It's on the second (new) one that we're going to install Windows 7 RC.

For Windows XP you'll need third party partitioning software. I suggest GParted Live CD:

1. Download the iso file for GParted Live CD and burn it to a CD (if you don't know how to burn an iso file, click here).
2. Reboot your computer with the CD in the CD-drive. (If your computer asks you whether you want to boot from the CD, say yes.)
3. GParted Live will boot up automatically. It will prompt you for a few things: at the first menu, choose "GParted Live (Default settings)" — if you can't press enter yet, just wait as it will choose this option automatically after a short while; then it will ask you about the keymap after a while — choose "Don't touch keymap"; then it will ask which language — type "02" for English and press Enter; then lastly it will ask you which mode you want — type "0" and press enter.
4. Click on the drive you want to shrink and click on the "Resize/Move" button. A window pops up.
5. Click and drag the right-hand black arrow to the left, until the desired size in the field next to "Free space following" is reached. (Seeing as Windows 7 will need at least 16 GB or so, I suggest that you make this size no less than 25 GB (25600 MB) to give it some room to breathe. Keep in mind that you will be able to access your other partition through Windows 7 RC too, so you don't need space for files on the partition that you're going to install Windows 7 RC on.)
6. Click on "Resize/Move".
7. Your hard drive will now show an "Unallocated" grey-coloured area with your original partition being smaller than it was before.
8. You now need to create a partition in this "Unallocated" area — click on the grey area so that it is highlighted and then click on "New".
9. A window pops up.
10. Specify what the size of the new partition should be (drag the right-hand black arrow until the size is reached in the "New size" field, or simply type it in).
11. Next to "filesystem", select "ntfs" from the drop-down.
12. In the area next to "Label", type in a name for the new drive.
13. Click on "Add".
14. GParted now knows what it needs to do but it hasn't actually done anything yet, so to implement all these changes, click on "Apply". At the prompt to confirm, click on "Apply" again.
15. When GParted tells you that everything has been done, you can close the program (click on the X in the top right corner, then double-click on the Exit button at the next screen, and finally click on "OK" when the small window pops up), remove the CD from the drive when prompted, and reboot your computer.
16. Your computer will now boot up into Windows XP as before, with the only perceptible change being that your computer now seems to have two hard drives instead of just one. It's on the second (new) one that we're going to install Windows 7 RC.

» Finally, time to install - on page 3!