> Is it possible to make m0n0wall act as a wireless accesspoint with an
802.11g wireless card ??

Hmm, pretty much anything with a Prism chip set will work great. See the
'chipset' column of this page
http://seattlewireless.net/index.cgi/Client_5fAdapters_5f802_5f11b for some
ideas. But those are 'b' cards, not 'g'. The equivalent list of g cards is:
http://seattlewireless.net/index.cgi/ClientAdapters_2f802_2e11g, but Atheros
is the main chipset maker here and I don't think freeBSD 4.9 (as used in
m0n0wall) supports Atheros yet - but I could easily be wrong!  Might be best
to stick with 'b' for now.  The extra throughput is mostly only useful if
you've got a pipe large enough to feed it with - cable or DSL in most parts
of the world won't come close.

A popular 'g' (and 'b') manufacturer is the Senao/EnGenius cards available
in many places, including here: http://www.netgate.com/80211g.html.

Configuring to make m0n0wall run the card as an AP is almost trivial once
you can confirm you have appropriate drivers for the card.

cheers, michael