[Nottingham] Wireless routers

[Ashley]

I am looking for advice and recomendations regarding wireless routers.
 It is to be installed in an old three story house (solid walls) and
needs to be powerful enough to reach all rooms.  I have never used a
wireless network before.

At a recent meeting a wireless router was discussed that runs Linux
and could be reprogrammed to output a higher power signal.  What make
/ model was it?

I am a rather concerned about security.  What security features should
I look for?

What is the best wireless secuity setup that can be used with XP home?
(not my choice!!!)

Can I block access to all but specified mac addresses?

Many thanks,
Ashley