If the 07 model is any indication for the 08, I would expect Toyota to announce sometime in the vicinity of August if any changes are planned for 08. Also, don't expect the 08 model to be available on the dealer lots until (depending on location) at least until Oct/Nov.
Toyota usually releases info in aug or sept and release the tacomas in oct/nov.
When I got my 2001 taco I bought mine first week that they were released sometime in oct 00 and when I go my 07 taco in Jan 07 I ordered it in Nov 06. after looking at the 07's through most of Oct 06.
So you got 5-6 months.