Deductions & credits

I purchased a computer for $1500 same year as my taxes. It is 100% for my rentals. I want to write it all off (it will be used for 5 future years) and NOT recapture depreciation. I may have a loss this year but I understand it will be carried forward. Next year I will have positive income. Can you point me out  where I can find THE FORM?
Can I split the use of the computer among my rentals or should I just apply the deduction to one rental?

THANKS!