Steve has an article on how to get up as soon as your alarm clock goes off. One thing that seems relevant is that the mind needs to wind down a little before trying to go to sleep.
For a start I'd suggest have a look at your pre sleep routine and look at what stimulus are present before the nap/core sleep such as noise, light, physical activity, mental activity... see if you can reduce those by reorganising your tasks.
As far as a disrupted nap/core sleep, have a look at your sleeping area and see if you can make it darker or quieter or more comfortable in any way.
I had the same problem with my nap just last night. I kept waking every 15 minutes. My nap is 9pm - 10:30 and I think I slept from 9:15-9:45 and then woke up, by 10:10 I hadn't got any more sleep so I got up. I kept to my 4.5 hour core sleep so tonight I should be tired enough that I will get to sleep for my nap on time.
Remember this is not a failure but an opportunity to learn.