> As long as it is standards compliant, you should be able to get it
> working.  Check their website for interoperability specs, some
> manufacturers have docs available that walk you through the process of
> getting their stuff to talk to other vendor's equipment.  Something like
> that should give you all the info you'll need.
>
>
I found this list on
http://www.zyxel.com/support/supportnote/zywall10_50_100/faq/vpn_faq.htm:
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We have tested ZyWALL successfully with the following third party VPN
gateways:
Cisco 1720 Router, IOS 12.2(2)XH, IP/ADSL/FW/IDS PLUS IPSEC 3DES
NetScreen 5, ScreenOS 2.6.0r6
SonicWALL SOHO 2
WatchGuard Firebox II
ZyXEL ZyWALL 100
Avaya VPN
Netopia VPN
III VPN
-----

That would proabably indicate that m0n0wall should also work?

Espen