I'd say do it ever 80,000-90,000 Kms or so. Some people do it sooner, but I personally don't think that's necessary, especially on the first one.
In my opinion, you are taking a big gamble if you aren't planning on replacing everything on that side of the engine, not just the timing belt! (i.e. you should replace the timing belt, balance belt, accessory belts, all pulleys, tensioners, etc., water pump, ...). The parts alone are approx. $600CDN if you order from the U.S. (e.g. Tallahasse Mitsubishi) or probably close to $1000 if you order locally (best to call and confirm that number though...
)
Labour should be $300-$400.
[ December 27, 2001: Message edited by: Jeff Mitchell ]