I left my key in the on position for a weak on my 2006 1800 vtx. My battery is dead should I buy a new battery or can I start this bike and recharge the battery I'd I ride for a few hours

Take the battery out, check your water levels. Give the battery a good deep cycle charge with a charger before you do anything else.

Yes, You could jump it and ride it for a hefty amount of time. However riding a bike with flat batteries can cause issues on the ECU if your bike model has Electronic Fuel Injection.As the EFI relies on a minimum amount of power to run the ECU(computer), at low revs some bikes are stubourn and rev irregularly to try and produce power from the alternator to compensate for the loss in power from the battery which loads down the electronics when it is flat. If you are going to go for a hefty ride to charge the battery, try to ride out on he open road somewhere and avoid high traffic areas as well as areas where you will need to start and stop frequently.