Dual boot XP and Vista(Vista installed first)

Dear friends,
I am Dinesh Agrwal,a new member of this group.
I am facing problems in making my laptop(Lenovo-7757 62q, Vista Home Basic) dual boot,with XP and Vista.
As instructed in a tutorial by William, I created a seperate partion and installed XP there.Then i rebooted my sytem with Vista recovery DVD,which came along with my laptop. When i booted from the DVD, there was no option for "repair my computer", thats why i chosen "Install".
It reinstalled vista. After that whenever i restart my laptop, there are two options to boot
1. Earlier version of Windows
2. windows vista

When i chosen 1.Earlier version of windows , an error message comes that file "ntlr" is missing or corrupt.

What should i do??

Someone has told me that if i modify vista or do anything with vista then Warranty of my laptop will not be applicable. Is it true???

Thanx in advance.

Dinesh.