I have 2 computers on wireless. How do I completely block internet access to one yet leave the other wireless and the lan computer alone?

Go to the RULES tab and select ADD NEW.
On STEP ONE select BLOCK and hit NEXT
On STEP TWO leave it at ANY SERVICE
On STEP THREE select the computer you want to keep off the internet in the first drop down box, and then select WAN(Internet) in the second drop down box. Click NEXT.
On STEP FOUR its up to you if you want to log connection attempts.
On STEP FIVE you can give it a name and hit FINISH.

It is best if you also go under the NETWORK tab and create a NETWORK OBJECT for this computer and then select the option to "Reserve a fixed IP address for this computer" so the IP address doesn't change at some point and render the rule obsolete.

Hope this helps.