It's not 10.3.3...
I've been experiecing a very symiler problem for some time now...
If I come into work with my iBook, then connect the ethernet & wake it up, it will not connect to the network. If I, on the other hand, wake it up, THEN connect the cable, it connects fine...
The same holds true if I let the system sleep while still connected to the network... The only 100% fool proof workaround I've found is to not use DHCP...
I dunno if it's some kind of setting or what, but this has been happening to me for as long as I can remember...