Odds in gambling-type situations such as dice-throwing are usually expressed as "so many to so many", as in '5 to 1' or '7 to 2' etc. In this case, a reasonable player should quote you the accurate odds of '8 to 1 against', as the figures in the above answers suggest. (Of course, a bookie wouldn't offer you those odds, as he has to build in a profit margin for himself!)
There are 6 x 6 = 36 possible outcomes, but only the following 4 outcomes produces totals to five:
1,4 2,3 3,2 4,1
That means that there are 36 - 4 = 32 ways in which the two dice can not roll a five. Therefore, the odds against rolling a five are 32-to-6 or (reducing) just over 5-to-1.
I think. Mebbe. Then again I just posted a question about odds myself, so what do I know?