A suggestions the first time you start it up make sure that the updates are not mirrored or enabled.
In the Apple Server Admin tool select Software Update the select Settings you will see a general tab make sure that Automatically mirror updates from Apple and Automatically enable updates are not selected click save and then start the service.
Once the service has started and everything seems fine and you have no errors in the software update log file select the updates tab and select the updates that you need or want to enable If you want to enable all of them that’s fin but only do a few at a time like 15 to 20 unless you have ample bandwidth available. As the server will go and download all the updates that are selected at the last glance I had that was about 4 GB
Once you have setup and configured your Apple OS X Tiger server for Software Updates you can check out the below information
If you have Apple Remote Desktop you can send a Unix command to change the software update URL. Some people have to change it in two locations. As per below
defaults write /Library/Preferences/com.apple.SoftwareUpdate CatalogURL http://update.server.com:8088/
defaults write /private/var/root/Library/Preferences/com.apple.SoftwareUpdate CatalogURL http://update.server.com:8088/
By what I have heard Apples Work Group Manager should information down to managed clients. But you can also use this great Application if you are Terminal shy. Software Update Enabler
I would assume that this also works with 10.5 server.