Byetta is a drug called Exenatide. This a drug that is often given as an add-on treatment to your usual diabetic meds (gliclizide and metformin or whatever) to help bring blood sugar levels under control. It's also supposed to aid in weight loss, but it's side effects include nausea, stomach upsets and vomitting and the like. It's an injectable drug, you take it like you would insulin, by subcutaneous injection into the skin around the middle. You would start of on a 5 microgram dose, twice daily with meals (to minimise the side effects), then after a month, if you're still happy and still need to get glucose levels under control, you may step up to 10 micrograms twice daily. It's very popular with our diabetes consultants.
I'm never actually taken the stuff (yet....), i just dispense it, but i hear that the nausea can get pretty bad.