And just to make sure we understand you....
In Enterprise Manager, you are right clicking on a database, selecting Properties, and going to the Options tab. Correct so far?
Now the confusing part, you say the OK button is disabled? What do you mean 'disabled'? Do you mean that when you change the Recovery Mode and click OK nothing changes?
If that's true, then I will guess you are trying to change the Recovery Mode of a system database. You can not change Master, TEMPDB, and I believe you can't change MSDB.
-SQLBill
Posting advice: FAQ481-4875