Gina,
Welcome to the ShopBot Forum. Be sure to look around a bit, especially in the Show & Tell area, where people showcase what they have made.

Part hold-down is practically the entire job when cutting on a CNC. I think as you start to grown in your CNC experience, you will find several methods will be required to hold down various materials and parts.

The absolutely simplest hold-down method is heavy duty/high traffic carpet tape with fiberglass weave in it. Ace Hardware sells it all over the country. Ace Hardware Product Page It is 2-sided, has aggressive adhesive and the fiberglass weave makes it easier to get off than regular 2-sided tape.

My recommendation would be to lay some strips of carpet tape right on your t-track bed, and then adhere a 1/2" sheet of MDF to the tape. Press it down well. This will be what we with larger machines call a spoilboard. You can then put strips of carpet tape down on top to hold down whatever material you want, then just peel it off when done. Super easy!

Home Depot and Lowes sell 1/4 sheets of MDF that you can cut down to the table size of your Desktop. Don't worry about gouging or messing up the MDF when you cut your parts - it is meant to get 'spoiled', hence the name, spoilboard. When it gets a little ratty, or you find it isn't as flat as you like, you can machine the whole surface flat using the TableTop Surfacer in SB3 under the Tools menu.

Hope that helps!

-B