As I recall when I set up mine, the security part lies in the way you set up the modem, not in the Mac. I have a Linksys, and walking thru the various help screens they provide. This is the critical one:
http://linksys.custhelp.com/cgi-bin/...?p_faqid=15841
You have to be connected by ethernet (wire connection to your cable modem) to set it up, then you are wireless after that. I have my desktop wired in (it has no wireless card anyway), but you could connect your laptop by ethernet just for the setup, then unhook it after you are done.
Oh, and name your system something other than "local cable company name here" or "Hot Studmuffin"! You'll just look goofy to all your neighbors!