I tried using Wireless Tether from the market. It runs and works but complains I don't have a netfilter enabled kernel. Is this a problem? I've also tried mynet in the Liberty Toolbox but so far, while my Xoom shows as a connected device, I've not been able to connect to any websites.
For mynet, looking at the Xoom I see:
security: wpa/wpa2 psk
signal strength: excellent
link speed: 54Mbps
IP address 192.168.1.136
So connection between Xoom and X seems fine. 3G signal on the X is at 3 bars and the X can browse the Internet with no problems.