Could also consider the offline Combo update package; Apple - Downloads - Mac OS X - Mac OS X Updates

I had to reinstall my Leopard a couple of days ago (archive install), after just purchasing the computer just over a week ago. System is running better now. Offline updates are safer/more reliable than online updates such as thru Software Update.

* After doing any system updates or installations, it is highly recommended to do a safe boot and repair permissions. Then reboot normally. SAFE Boot & Repair Permissions