In dec 2007 we bought a new motohome to live in while travelling for work as a travel nurse. I heard that Pres Bush Sr passed a law allowing the deduction of the purchase price of the motorhome over 4 years.. it seems hard to believe but I searched online but found nothing.. it this deduction valid??

A motorhome may be considered a SECOND home for tax purposes, which means you can deduct the interest paid on the loan for the motor home as an intemized deduction on Schedule A.

You could possibly depreciate the motor home on Form 4265 if you got paid as an independent contractor under Form 1099-MISC for your nursing work.

See also:
Publication 587 (2008), Business Use of Your Home

It all depends on the circumstances. See the instructions for Form 4562:
Instructions for Form 4562 (2009)