timing belt questions

I just bought a 2000 V6 EC TRD 5 spd w/ 69000 miles. It has no maintenance records or manuals. When should I change the timing belt? How can I check to see if it has been done already? Is it difficult to change or should I just write a check and have someone do it?

Also what's the feeling about a Gibson SS cat back and a B&M shifter for this vehicle?

BTW, Great forum

Yea, can we get a sampling of when (Miles on Vehicle) everyone has changed their "Timing Belt"?