A few questions.

Zencart was listed on paypal as having support for paypal payments pro, and it was the only cart I could find that was free that supported this. Does it in fact support payments pro and how do you set it up?

Secondly, all I really want to make is a single-page order form for my website, with several options.
-3 Drop down boxes with options that affect/don't affect the price
-Two text boxes for customer requests on the customization of the order
-Several check boxes for add-ons to the order.

Can this cart support such an order form? Or is it just for a store-front-based type site?

Zen Cart is designed as an all-in-one site/cart software. While it can be simplified a great deal depending on your needs. it is not a drop-in shopping cart for an existing site. However, it's fairly straightforward to rebuild your existing site in Zen Cart and then you have all of its abilities to grow into.

PayPal Website Payments Pro was added to Zen Cart as of v1.3.8. If you need to ask about setting it up, look in the PayPal Website Payments Pro support section of the Configuring the Zen Cart Admin part of this forum.

Rob