[needhelp]

The problem is with a computer my friend bought a couple of weeks ago. Had Windows XP and Vista installed on two seperate drives but only came with the original XP disc and no Vista disc.Of course the computer always booted by default into Vista

All went well until a couple of days ago when message comes up on screen saying that Vista was not a valid copy would stop workng. Needless to say the computer wont boot into VIsta.
okay so here is the problem. when booting up the computer he is still coming up with the option to boot into Vista and he has to manually select XP or the computer tries to boot into Vista .
I have tried to help him by going into msconfig in XP and changing the boot ini to boot XP instead of Vista as default, but it tells me that Vista option can only be changed with BCDEDIT and not in the usual way (Dont know what BCDEDIT is or how I get into it.)
I tried to format the disc with Vista on it from disk management in XP but it would not let me format the drive. said it was being used, tried to force the format but it wouldnt let me do that either.
So, ideally what he wants is to leave the disc with XP on as it is now and format the disc with Vista on it so he can just use it for storage as a second hard drive. I guess what I need to know is.

How do I get rid of the duel boot up option so the computer will only boot to XP

and how do I format the hard drive with the pirate Vista on it and make it a clean formatted drive again.

I am reluctant to put the disc with Vista on it onto one of my computers to format it in case it installs the duel boot option on my computer and I get the same problem as he is getting now.
The discs are formatted NTFS The conmputer doesnt have a floppy drive, only CD ROM drives.

So what do I do with this one. I feel sorry for my friend because he is not the one who installed the pirate copy of Vista on the computer and would not know how to install a program on the comp. he is completely computer illiterate

The guy who sold him the computer is acting dum and says that he only had bought the compute recently and Vista was on the computer when he bought it.

Needhelp on this one urgently.