I did it a couple of months ago. First you will need Winzip, then you just take all the components of your theme and create a zip file.
Once you have your zip file go to WC, click the upload link which will take to a page that lists the various libraries.
Click on the library that corresponds to your theme, fill in the boxes, click the 'upload theme' button, and in a few days you be notified as to whether your theme has been accepted to the site.
I think that just about covers it. Just be prepared to wait. It took close to two weeks for me to hear back from them. They're not ignoring you, they just receive a lot of submissions and it takes time to consider them all.