So, now that you have created your theme using this tutorial;
How to: Create Your Own Winterboard Theme!
You are ready to submit your theme to Cydia for the world to download and admire!
(I will show you how to submit to modmyi.com)
After you create your theme, you will want to use SSH to get it to your computer.
Follow this guide for how to ssh: HOW TO - Use Secure Shell (SSH) with the iPad
So, using winscp (or other ssh program) navigate to VAR/STASH?Themes.(whatever)
Drag and drop your theme folder to your desktop.
Zip it up!
No really, you need to make it a zip file.
In windoze, right click on the folder and hover over "send to", and click on "compressed (zipped) folder"
Now on your desktop you should have a compressed version of your themes folder.
Open your browser and go to modmyi.com
Click on "Dev portal" on the top right.
Fill out the form and just browse for your theme you zipped to your desktop!
In 24 hours you should get an email from modmyi saying your theme has been accepted and should show within another 24 hors in cydia!