I just got my Dual 2.3 G5 yesterday. Man is it fast!!! However, when it downloaded all the software updates, it took a long time. Also, when I was downloading the Microsoft Office updates, it took forever. I have a high-speed cable internet connection that's conencted with an ethernet cable. Is it normal for updates to take a long time?
I do all the software updates via stand-alone updates. Then when I have everything, and the system is backed up first, I make sure the primary drive is okay (or run fsck and Applejack) before applying anything.
Is it possible that your network settings need changing? that your modem or router/switch are the issue? I assume you would use either modem/router/switch or some combination.
Also, the amount of memory affects how long it takes to apply and optimize updates, as well as the speed of the boot drive, how much free space etc.