Uploading from CS3 Bridge is a snap. You can use the Uploader on SmugMug itself, and drag JPGs directly from Bridge to the uploader. Or you can upload directly from within Bridge.
Note: Uploading from Bridge CS4, CS5, and CS6 is not supported.
First, open CS3 Bridge. Then Click Tools > Photoshop Services > Automatically check for services.
If you don't see the Photoshop Services option, open your Bridge CS3 Preferences, then highlight "Startup Scripts." You should see a checkbox that says "Photoshop Services." Check this box, click Ok, then restart Bridge.
After that's complete, you should see SmugMug under Tools > Photoshop Services > Online Portfolios and Galleries > Publish Photos with SmugMug.
Highlight the photo or photos you want top upload in Bridge, then click Publish Photos with SmugMug.
You'll get a login screen: