To Witt in DC:
First of all, thanks for the compliment on my socks, I am glad you like them. Now to the technical question:
The tubular cast-on I used for the "Embossed leaves socks" is described in Montse Stanley's "Knitter's Handbook", page 78. It is called "Two-strand tubular cast-on" and is worked with two strands of the same yarn.
I know from experience that it is quite impossible to explain this method without showing it - so I won't even try. For now.
Come back in the next couple of days for a tutorial on the two-strand tubular cast-on - with pictures and the whole shebang. If this takes too long, if you are an incredibly impatient knitter and want to knit the socks right away and don't care too much about this stretchy, very useful cast-on (in my opinion, anyways) just go with the long-tail one, it works too.