Mini Server, bridging Ethernet and Airport ?

Question

Hy there.
I´ve got a Mini running 10.5 Server with Ethernet en0 and Airport. To set up for testing I´m want to set the Mini as a wireless bridge. With NAT and the gateway assistant, I`m only apple to set up routing with a block Airport -> Ethernet. In detail:
Ethernet 192.168.100.x
Airport 192.168.1.x with NAT and DHCP
Clients connected to Airport aren`t able to go to the 192.168.100.x network.
Is it possible to bridge the two nic´s?
Aggregation won´t work on Airport.
Thanks for reply.

Answer 1

The network configuration details and the goals aren't entirely clear (to me) here, so I'm going to shot-gun several answers here. I (also) don't know how experienced you are with IP networking and terminology; apologies in advance.
"Bridging" occurs at layer 2 and is relatively comparable to a network cable or such and thus arguably transparent to network traffic (you can't "see" a bridge at the network layer any more than you can "see" a hunk of network cable), where "Routing" is layer 3 and typically involves IP addresses and a routing stack. Bridging doesn't involve an IP network address for the intermediate device, where routing does.
Your Mac Mini here lacks bridging capabilities, and would be either a non-routing host or (with two NICs and a requirement to route traffic through) an IP router.
Various Airport devices can be configured as routers or as bridges. The default configuration is the former; as a WiFi router. If you want to run the Airport as a bridge, then it won't have an IP address. Various folks will refer to a WiFi device set up as a bridge as an Access Point, as well.
Depending on the subnet configuration (and I will here assume you are using two subnets here, the 192.168.1.0/24 and 192.168.100.0/24 subnets) and if you're using your Airport as a router in 192.168.100.0/24, you'll need to set up the Mac Mini or another IP router-capable device in 192.168.1.0/24 as the default IP gateway (default router) within the Airport configuration. That default gateway (router) will itself need a path to the wider Internet, and routes to other subnets.
Getting a Mac to function as a router and as a network gateway (and with NAT and firewall) is possible, but you'll have to set up the default routes appropriately. It's generally (far!) easier to use an external box for this purpose; a dedicated firewall and NAT and router box. It's also something I typically prefer; having users and software configuration changes and the usual sorts of activity found on a Mac OS X or Mac OS X Server occurring on a firewall can risk (accidentally, unintentionally) open up a remote exposure.
If you want to use link aggregation with Mac OS X Server, then you'll usually need a network switch capable of IEEE 802.3ad link aggregation. AFAIK, Airport doesn't provide link aggregation.
Apropos of nothing else in this reply, if you're planning to eventually use VPNs (tunnels), I'd also suggest getting out of 192.168.0.0/16 address range (and into 10.0.0.0/8 or 172.16.0.0/12, per RFC 1918), everybody uses that, and various tunnels need unique subnets both locally and on the target end of the connection.
Here's an intro to [networking, routers and firewall|http://labs.hoffmanlabs.com/node/275] pieces, and a previous discussion of [IEEE 802.3ad link aggregation, BGP and such|http://discussions.apple.com/thread.jspa?messageID=9141545] here in the forums.
It's my general preference to block access to the LAN with a dedicated firewall/NAT/router box for the reasons described above as well as other reasons; that box can act as the default gateway for all subnets, as well.
If I've entirely missed your question with the above answer(s), hopefully the above can help us get a little closer to your particular goal and an appropriate solution.