I felt the same way about running. At first I wanted to do it but my body couldn't get past a certain point.
I started off doing 20 minutes at an 3 easy pace (4.3 -4.5 mph) and then I was able to up that to 30 minutes. It took me a few weeks, though. Once I got to 30 minutes I increased the mph but not the time. So, I was covering a further distance in the same amount of time. I did that for another few weeks. Then I started to focus on distance. I wanted to do 3 miles. Turned out that to do that I had to run for close to 45 minutes. Then I increased it 4 miles while simultaneously increasing my mph. Again, I was running faster but farther for roughly the same amount of time. It took me almost 3.5 months but I'm now able to run 5 miles in about 55 minutes. Sometimes I go faster (increasing my mph every so often for 1/2 mile here or there). It all depends on how I feel. I also split up my mileage: I'll do half on the elliptical and the other half on the treadmill.
It definitely helped me to work my way up to my current distance/time. Alternating between increasing distance ran in the same time amount and then overall distance was a big help in the barrier I had to increasing my overall sustained cardio sessions.
Another thing that worked great for me was my iPod! I custom mixed some great heart pumping songs and made sure that I had some of the really great ones, that would get me moving, at a time when I knew I'd need the energy. So, it works out that just when I want to stop a great song will come on and I'll tell myself, "just run through this song" and before I know it I've kept going.
Sorry to have rambled...hope this help!