Hi Sandeep,
I would use authorized test material so you can trust you are not unintentially cheating.
http://www.measureup.com provide practice tests for 70-448 and if you join their mailing list they give regular 50-60% discounts.
The Microsoft Training Guide is very good for thiis exam and also includes pratice tests.
You can get the ebook version online now with the cdrom download from
http://www.oreilly.com
Good luck and kind regards,
Ozzy Geoff