Until this stuff is in lenny-backports itself, add this to your sources.list:

deb http://people.debian.org/~jonny/backports ./

These packages use a lot of other packages already in lenny-backports, so be sure to also add this to your sources.list:

deb http://backports.debian.org/debian-backports lenny-backports main

 Name                                               Last modified      Size  Description
 Parent Directory                                                        -   
 HEADER.html                                        2011-01-07 15:19  431   
 Packages                                           2011-01-24 16:08   53K  
 Packages.gz                                        2011-01-24 16:09  7.2K  
 Sources                                            2011-01-24 16:09  9.9K  
 Sources.gz                                         2011-01-24 16:09  3.1K  
 amd64/                                             2011-01-24 08:50    -   
 gir-repository_0.6.5-7~bpo50+2.dsc                 2011-01-24 16:05  1.6K  
 gir-repository_0.6.5-7~bpo50+2.tar.gz              2011-01-24 16:05  323K  
 glib2.0_2.24.2-1~bpo50+2.diff.gz                   2011-01-14 14:37   40K  
 glib2.0_2.24.2-1~bpo50+2.dsc                       2011-01-14 14:37  2.4K  
 glib2.0_2.24.2.orig.tar.gz                         2011-01-14 14:37  7.3M  
 gtk+2.0_2.20.1-2~bpo50+1.diff.gz                   2011-01-20 11:17  251K  
 gtk+2.0_2.20.1-2~bpo50+1.dsc                       2011-01-20 11:17  2.1K  
 gtk+2.0_2.20.1.orig.tar.gz                         2011-01-20 11:18   27M  
 i386/                                              2011-01-24 16:08    -   
 pygi_0.6.0-1~bpo50+1.debian.tar.gz                 2011-01-06 20:12  3.0K  
 pygi_0.6.0-1~bpo50+1.dsc                           2011-01-24 08:34  959   
 pygi_0.6.0-1~bpo50+1.tar.gz                        2011-01-24 08:34  890K  
 pygi_0.6.0.orig.tar.gz                             2011-01-06 20:12  379K  
 pygobject_2.21.4+is.2.21.3-1~bpo50+1.debian.tar.gz 2011-01-06 20:06  109K  
 pygobject_2.21.4+is.2.21.3-1~bpo50+1.dsc           2011-01-24 08:34  1.1K  
 pygobject_2.21.4+is.2.21.3-1~bpo50+1.tar.gz        2011-01-24 08:34  2.4M  
 pygobject_2.21.4+is.2.21.3.orig.tar.gz             2011-01-06 20:07  889K  
 pywebkitgtk_1.1.8-1~bpo50+1.debian.tar.gz          2011-01-06 20:15  4.5K  
 pywebkitgtk_1.1.8-1~bpo50+1.dsc                    2011-01-24 08:34  892   
 pywebkitgtk_1.1.8-1~bpo50+1.tar.gz                 2011-01-24 08:34  857K  
 pywebkitgtk_1.1.8.orig.tar.gz                      2011-01-06 20:15  334K  
 webkit_1.2.5-2~bpo50+1.debian.tar.gz               2011-01-06 21:22   35K  
 webkit_1.2.5-2~bpo50+1.dsc                         2011-01-24 08:37  1.2K  
 webkit_1.2.5-2~bpo50+1.tar.gz                      2011-01-24 08:38   17M  
 webkit_1.2.5.orig.tar.gz                           2011-01-06 21:23  6.4M