Hi T. - my 5mo did the same thing until recently, when i also read 2 books: the first is 'secrets of the baby whisperer' (also has a sequel called 'the baby whisperer solves all your problems') and the second is the one another poster mentioned - healthy sleep habits,happy child. both books are useful, but i would definitely read them BOTH so you can figure out what is right for you. i personally am not at this point comfortable letting my child cry alone in her room, and the baby whisperer book has some alternatives to that. what i do now, which helps my dd, is when she wakes up at the 30 min mark, i wait until she cries, then i go in and pick her up, give her a binkie, make sure her swaddle is on tight, and hold her sort of sideways in my arms until she falls back asleep. it has gotten much, much easier in the past few weeks. at first she would cry and wiggle, and i would have to jiggle her. i stopped jiggling when she calmed, and started again when she fussed. i put her down when she's almost asleep - as in, her eyes have been closed for a few minutes, her breathing is deeper, but she knows she's being put down. if she cries again, i pick her up and do it again.
that's what i do,but the baby whisperer book has another method, the pick up/put down method, to train your child to go back to sleep alone. i tried it, but i couldn't get it to work - maybe b/c i was doing it wrong, or dh was doing it wrong perhaps. but the website babywhisperer.com has some great info and advice about some of these methods, including the one i use (the "gradual" method").
anyway, gradually she has been able to go back to sleep much more quickly with much less intervention. there have even been a few times lately when she just needs me to give her the binkie.
but i think that sleep to wake method sounds good, which the other poster mentioned too - i will look that up in the book and try it. what the book says is that these catnaps indicate that the baby is too overstimulated right before the nap, and needs a longer and calmer wind-down period. i find better wind-down does help dd sleep better, and yes - more sleep helps too. the baby whisperer book will help you get your baby on a schedule, too - mine was not until i got this book.
so - hope this helps, good luck!!!
T.