Here is a similar example:
http://www.borugroup.com/vtiger_quickbooks.html
You can see that they have an ‘add to quickbooks’ button.
I would need a similar button, on the CONTACT page that said “Accept Payment”
This button would just open up a html link to a webform. The contact information from vtiger needs to be included in the link so it can poplulate the webform. Basic info sent would be name & billing address.
The webform will be used to charge their credit card.