It's been seven years since the first post. Mactheturk may have learned to yodel, given up the idea or passed away since then. However, somebody must be interested, since this thread has reappeared.

This site has some useable tips

http://www.wikihow.com/Yodel

[Is that how you spell useable?]

A person who followed these tips and listened to samples of good yodeling could really get somewhere.
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This site has some good samples, though they are too short.

http://www.yuckles.com/yodel.htm

The sample "Joy of Yodeling" shows a feature that nobody mentions: the almost instantaneous stopping and starting of sound.

It seems to me that yodeling involves a rather tight throat, especially for men. Don't overdo it, or you could hurt yourself.