Afternoon chaps

It looks like I need to set up my MacBook Pro to be a temporary router for my flat for about a month.  I've used Airport to create a wireless network and shared internet over it, WEP40 with a very basic password (in fact, it only allows a 5 digit password... no more, no less).  Problem is, it keeps randomly dropping its security and becoming an unsecured wireless network.  Bad.  It also requires manually connecting to every time one powers on their computer.

Googling around, I can't seem to find any software wireless router options that aren't ten years old.  Does anyone know of any decent free solutions?