iggy, it's not 100% clear what exactly you're looking for. Are you looking for the order, once it's placed, to be transmitted via fax rather than email?
I'm not familiar with that orderform, but I am familiar with a free shopping cart system that directly interfaces with PayPal, as well as Mal's with which a number of options are available.
The primary consideration in this issue is that whether the information is to be sent by email or by fax, if a credit card number is to be included as part of the transmitted data, it will need to be encrypted.
I know that info can be sent by fax via email, from a PC, but which protocol would be used to transmit server to fax has to get into the issue of whether PGP can be used - otherwise it's too much of a risk with sensitive information for ecommerce usage.
If you're interested in that commercial script, then they should be able and willing to support your question about it's functionality prior to purchase - I'd assume they would know the answer.