Direct connect with a crossover cable.
I think the Roku will eventually timeout and have a default IP. Look that up on screen.
Configure your laptop for a static IP in the same subnet.
Then you should be able to telnet into the Roku and configure it for a static IP on your normal network.
The RS232 port SHOULD act as a "console". You would connect a serial cable from there to your laptop, open a Hyperterminal, and power up the Roku. You should see bootup process in Hyperterminal, and be able to interact via laptop keyboard, and configure static IP that way. I could swear I've seen more about doing that either here in the forum's or in the FAQ's.
HD-1500 RevB #1 (media room)
Mitsubishi WD-62528 62" LCD RPTV
Kenwood VR-407 receiver w/PSB Alpha's
PS/3 60GB (now 250GB) w/750GB Seagate ext
HD-1000 RevB #2 (bedroom)
Visco 32" LCD
AR 2.1 audio system