1 - Download Gallery2Flickr from this website:
2 - For Windows users, use Winrar or similar software to extract all the files from the downloaded archive. This will create a folder named "Gallery2Flickr" which contains all the files for the Gallery2Flickr module.
3 - Launch your favorite FTP program and connect to the site where you have installed Gallery.
4 - Using your FTP program, navigate to the directory on the site where you installed Gallery, then navigate to the "modules" directory.
5 - Transfer (i.e., upload) the Gallery2Flickr folder (not just the contents of the folder but the folder itself) from your computer to your site's modules directory.
6 - When the transfer is complete, visually confirm the Gallery2Flickr folder is under the modules folder.
7 - Quit the FTP program and launch your browser. Navigate to the site where Gallery is installed and login as the administrator.
8 - After logging in as administrator, look in the Admin Options panel found on the left edge of the screen and click on PLUGINS.
9 - After the plugins page finishes loading, scroll down to the IMPORT section. Gallery2Flickr should be listed there.
10 - Click the INSTALL link found at the far right of the row where Gallery2Flickr is listed.
11 - Do the happy dance, you're done installing Gallery2Flickr.