I brought a toshiba from the pawn shop and i tried to change from windows xp to windows vista how can i find a hard drive disk to install windows vista

You don't need to replace the Hard drive in the laptop, you can usually upgrade, or install vista from the CD-ROM / DVD-Rom.

If your laptop does not have a DVD drive to install vista, you may use file sharing to install it from another computer on the network. To do this follow these steps:

1) Place the Vista DVD in second computer
2) right-click on the DVD-drive that has the Vista DVD in it, and select " Share..."
3) You may need to press the "Advanced sharing" button to enable sharing, if so, do that, and just hit the " apply " button
4) OK out of all of those menues
5) on your laptop open " my computer" and click the " map network drive "
6) browse to the location of your drive on the other computer, and click " OK "
7) install Windows vista

If you do however need a new hard drive for your laptop, you can usually get them from any PC store such as Bestbuy, fry's, or online from places such as NewEGG.com, and Tigerdirect.com.

You will need to know what type of hard drive you have, and how to replace it. The manual for your laptop usually has this type of information.

SIDE NOTE:
When putting Vista on a laptop, be sure it meets the minimum requirements.