Hello...
I have DV 2000 series notebook and dual OS.
first i have installed XP and then I have installed Vista. Now i like Vista very much and want to remove XP, but i really don't know what is process .

So can any one help me and tell step by step process to make one OS as Vista ?

Thanks in Advance.

Go here and get DBAN, follow the instructions the website carefully. Once DBAN has finished it's work, re-install Vista...

DBAN Download | Darik's Boot And Nuke

Or u could just leave XP and Vista on but get Vista Boot Pro here

VistaBootPRO - Go PRO with Microsoft Windows Vista Boot Manager

and use it to set Vista as default OS and set the choose which OS to boot option to 0.

That way u dont have to go through the whole formatting and installing thing.

Or u could get Vista Boot Pro and use it to set Vista as the default OS and set the choose which OS to boot time option to 0 seconds. It'd save u the bother of formatting and reinstalling the OS.