Place yourself in the directory trunk/packages of your working copy of the SVN repository. Create a directory with the same name as your source package (let's say, my-package), and subdirectories tarballs and trunk. Put the current upstream tarball in tarballs, and the current debian directory with all its relevant files in trunk. This should now look like this:
trunk/packages/my_package tarballs my_package_1.2.3.orig.tar.gz trunk debian changelog control copyright patches 00_list 01_patch1.dpatch ... ...
If everything is in order you can do a svn add my_package from the trunk/packages directory, and eventually svn commit.