C25K on a treadmill?
 

Has anyone done it this way? If so, what speeds did you use for the different levels? Thanks!

I do! I walk at 4.0 mph and run at 6.5-7mph. Normally on a 1.5 or 2 incline. When I go at those speeds I sweat like a pig, and feel like puking when I'm running but I can finish. Seriously, do whatever feels challenging without feeling like you're gonna faint. You'll have plenty of time to mess around with speeds as you go through the program.

I just started doing this. I am walking at 3.0 - 3.2 and jogging at 4.3 - 4.6. I am a lot slower than the previous poster but I think a lot depends on leg length and fitness level. I hope to be able to increase my speeds as I get thinner and more fit.

I'm more like Sheena, I walk at 3.0-3.3 and I usually jog at 5.0
I would definitely say DO NOT WORRY about running fast, at all. It's not the point. As long as you're "jogging," even if it is at 3 miles per hour, it's fine. To me, the C25k program is about increasing the amount of time you can spend jogging at any speed that you can keep going at. Once you get your endurance up, then you can maybe try increasing your speed.