Afterwards

1. Apply the theme to your computer by double clicking and take a screenshot of it on your desktop with the Print Screen button on your keyboard (PrntSc).

2. Go into your preferred photo editing application (windows 7 comes with Paint if you don't have one). Paste it into a new document. Resize the image to 503x314 and then save it somewhere that you'll remember.

3. After logging in on this site, click Create Content on the new area that appears on the left. Click Windows 7 Themes.

4. Start uploading themes and follow the instructions on this site.