Yes, that (what you want to do...) is exactly what the big enjoyment of WiFi Tether is.
I know that on some tether apps there is a security section in the menu, but I believe most are defaulted to allow anyone (computer) to "see" the Android Wireless Tether.
If you are having these complex difficulties, I suggest that it is your computer that needs some settings tweaked.
Are you running Vista? (+10 points for difficulty & PITA-ness right there, if you are. Lol!)