Beating a sniffer on home wireless ?

[tincture]

I believe my wireless internet activity is being intercepted by my roommate. I don't suspect malicious intent necessarily, I'm merely interested in maintaining privacy.No evidence of hacking, and I do have firewall and sharing configured to block such.

Set-Up:

Shared linksys wireless router is situated in his space. Comcast broadband.

I'm using a powerbook G4 with Airport.

Is there a way to block interception assuming continued sharing of the account?

Change IP address? I understand the main account has one IP address ...

Proxy?

Once my IP is determined, can a sniffer intercept all my activity whether local on the WiFi in question; or if I am connecting through some other access point?

Is there software available for discovering a sniffer app operating in close proximity to our house?

Thanks