[Lisa R.]

Same as casting on any other number...you make sure you have enough yarn for your tail (the rule of thumb I was taught is to wrap the yarn the number of stitches and leave a little extra--a bit of a pain with that many stitches, of course).

Anyway, you then just start casting on as usual. If you want, you can use stitch markers every 10-20 stitches so you don't have to keep recounting from scratch to see if you have the right number.