Just a quick note: Don’t even think (really, no kidding!) about doing the remote installation via W-LAN (at least with if you can’t use 802.11n). Even with Gigabit Ethernet it takes ages:
(Doesn’t look too bad, huh. But: the estimated time remaining is steadily counting up, not down.)
There’s a thing that I experienced on two different Macs (Late ’06 MacBook and Late ’08 MacBook Air, both 10.5.7) at the same time: Software Update caused the whole system to hang after I had chosen to install the updates. No app would launch anymore, even a shutdown wasn’t possible.
Deleting /Library/Preferences/com.apple.SoftwareUpdate.plist did the trick and everything’s fine again.