How To Install Xp On Pre-loaded Vista System

Hey Pals I M Plannin 2 Buy A New Laptop(most Probably Dell 1520)
They Are Providing Vista Wid Da System And Only 1 Partition Of 160gb
I Want To Make 4 Partitions Of Da Drive And Install Windows Xp On One Of Da Partitions And Dual Boot Vista N Win Xp
Plz Help Me How To Do This.....
I Wud Be Highly Obliged......