I've posted this before, but here is a realy good board for discussions around CPAP machines:
http://www.cpaptalk.com/

One theme you will see there is that a lot of Drs and Medical supply companies really don't understand the features & advantages of different machines and masks. I HIGHLY recommend that if you are going into this area, do a lot of research and be educated. To paraphase someone from the board: "No one, not your Dr, not you sleep clinician, not your equipment provider has as much interest as YOU in getting you problem resolved"

I have used the following company for my stuff and have had very good experiences with them:
http://www.cpap.com/

My machine broke, I called them on Monday morning, they had a replacement machine to me Tue (and since they were out of stock on the machine I ordered, they upgraded me for free!)