If you're logged in over on Wincustomize.com, you simply...
1. Click the 'Submit to Gallery' link below your screename
2. Select the 'Poitical Candidates' library from the dropdown list
3. Fill in all the fields: Skin name is the name of the candidate, the image is just the picture the galaxy uses, and the candidate file is located in the candidates/packages directory (and does not need to be in a zip file).
Pending approval (I'll be moderating and help you as necessary) your candidates will be available for other players to download, rate, and comment on.
I'll try to get a more in-depth tutorial on the Candidates Library on monday. 
Hope this helps in the meantime!