Oops, sorry Liff. Yes, that's it. If they start crying as you put them down then put them all the way down but then pick up again and repeat!
Here's how it went for us in a planned 2 hour nap (naps disturbed due to jet lag):
Day 1: DS wakes after one hour. PU/PD about 15 times over 20 minutes. DS went down and then slept for 30 mins. Then woke. PU/PD for last 10 minutes of nap
Day 2: DS wakes after one hour. PU/PD about 10 times (approx) over 10 minutes. Then slept for 50 minutes until I woke him at end of nap.
Day 3: DS wakes after one hour. I go up and put the dummy in, he goes back to sleep. Same again about 30 minutes later.
Day 4: DS wakes after one hour. I put dummy in. He sleeps until end of nap.
Day 5: DS sleeps for entire nap.
...so basically takes some persistence but it worked in the end.
Baby whisperer book covers in detail. Or see www.babywhisperer.com/babywhisperer.html