If you own two homes One is your primary the other you rented.
07 was the first year as a rental While trying to find a rentor the house was empty for some time and it has taken 5 months to rent can you claim loss of rent as a cost for those five months?

You can start claiming the expenses on the rental house (to include depreciation) the day you started preparing the house to be a rental, even if it is up to a year prior to actually renting the house to a tenant.

If you're asking whether "loss of rent" is some sort of expense you can deduct - no. You can only deduct true out-of-pocket expenses and depreciation.