I have sold quite a bit (to say the least) over webinars this year. some info

1 - Pauls blog post on GTW processing is the only workflow that works. Follow it. I had to figure it out on my own to the same result as well
2 - A custom signup page with a video intro by the host can convert better (30-50%) than the standard GTW signup form (25% average) You can use FusionHQ or hack up your own script to blow the GTW signup into a squeeze. You should also be co-regging the leads into your autoresponder as well
3 - Live demo if you are selling a software works best. (I have never used a powerpoint)
4 - I will let these testing numbers speak for it self. On a $1k product. ... Open the cart at the end of the webinar - %3 conversions. or... open the cart to the first XX people to buy = 15% conversions. need a strong CTA
5 - mail the replay while opening the payment plan the next day.

You have just been given gold. Read carefully the 5 points above and mint yourself.