If you want to Dual Boot and you have only one drive, C: and enough free space, 20 gigs (ok) 40 Gigs (better) you can use the

Diskpart tool to shrink your drive down so you can install Vista on a seperate partition to enjoy and test your programs.

When you boot your Vista cd and get the Install screen, there is an option to repair the computer all the way at the bottom. It

will do a search and a window will pop up.
Ignore any message there and press the [Next] button.
You will get a menu with Command Prompt being one of the menu items.

Select Command Prompt

Then select the drive where your CD Disk is at. (In my case it was drive D, so I put D

When in D: type CD Boot

Type in Diskpart

In Diskpart, Type in List Disk

You should then see your full partition.

Type in Select disk 0

Now type in List partition

You should see Partion 1

Type in Select Partition 1

The next command is Shrink

The program will now show you how much you can shrink your C: drive. Mine showed 23 gigs. This was because I had some unfragmented

files at that far end and it would not shrink past that point. I recommend defraging your C: Drive before you try this.

Now to set that new partition, type in

Shrink desired=23000 or whatever equivalent you got.

If the shrink says you have 34 gigs type in 34000

The new partition is set, and you exit the usual way by clicking on the X at the top right of the window.

Click on the X again at the next window to return you to the Install option.

At the install option you will be able to choose the new partition to install Vista.

The dual boot will fix itself and you are ready to go.

It sounds complicated, but is actually very easy.
Microsoft will talk you through it if you give them a call.