This is how you partition your hard disk.
- Click "start" followed by a right click on "computer" and click "manage" on your vista system.
- Now click disk management. you will see your primary disk(Disk0) size.
- Right click on it and select shrink volume option.
- System will calculate the amount of shrink space available. select the value you will be needing for ubuntu.
- When you load your unbuntu CD during the installation when asked use the guided use of largest free space.
Other alternative is the Sun Virtual box which needs no disk shrinkage. There is an easy installation procedure available online. Just google Sun virtual box and get started.
good luck ...........