As mbeach states, warranty begins from the initial "in service" date or when the 1st owner takes delivery.

The 1st owner has a 10 year/120K mile warranty that is non-transferable except to immediate family members, as is clearly stated in the warranty guide that comes with new Isuzus. The basic drivetrain warranty is 5 year/60K miles and is not affected by change in ownership as far as I can discern in any of the paperwork.

If you can't easily determine the initial delivery date of your VX give CarFax a shot as they'll show the original date of registration which should get you within 30 days of the delivery date.