How to purchase coins with Bitinstant with Mt.Gox / Dwolla?

[opentoe]

I have a fully verified Mt.Gox account. I also have a Dwolla account. I need to buy some bitcoin using Bitinstant, but finding the process odd. Where does the funding come from? I have a bank account attached to my Dwolla account, but Mt. Gox doesn't have bank account funding. What is the process/procedure to buy bitcoin with Bitinstant using Dwolla/Mt.Gox? Do I need to fund my Dwolla account, then send the funds over to Mt.Gox or somehow? If I could just add funds to my Mt. Gox I'd be ok, but I can't find a way to fund that account to buy bitcoin.

Thanks