How to reduce the 30sec. wait time while dual booting OS?

Hello everybody!
In my Laptop I am having two operating systems so whenever i switch on my laptop or re-start, it will wait for around 30 Sec and ask me to choose one from those O/S.
My question is; Is there any way to reduce this timing (30Sec) or i want to remove this option and directly load my XP O/S when i switch on my laptop.
Please help me.
