How do remove really old tape ?

I've got a 96 windstar. The backside window broke 1 sept 07'
 I taped it up with (beige) packing tape when it happened.
The tape served well all winter. I replaced the window mar 08.

The freaking tape won't come off the body/paint of the van.!

I dont want to use a razor to scrape it off. What solvent or
 chemical will dissolve old tape without screwing up the
 paint?

Thanks!