Assuming %1 is supposed to be a file (or list of files) then my ShellExtensions plugin (see the link to the CBIL project page in my sig, win32 binaries at the download page) will be well suited to your needs. This plugin allows you to add custom commands to the main menu and context menus (when you right click on files in the project page or in an open file's editing pane or in the file browser that is included in the plugin).
The command line supports a few useful variables, such as $dir, $file and $inputstr. $dir and $file is the file or directory name that the user has right clicked on. For example, you could specify the following command
svn commit $dir -m "$inputstr{Enter your commit message}"
which will run an svn commit on the selected directory and prompt you for a message in a dialog box.
