Network Configuration with WRT54G

Hi,

I'm looking for a solution to provide a decently secured wireless
connection.

I have a Windows 2003 Server with ISA Server, Radius Server (MS IAS) and
DHCP.
I wanted to use a WRT54G for this purpose.

I have an existing LAN using IP addresses 192.168.20.13 for the Win2003
server.

I wanted to connect the WRT54G with the 'Internet' connection to this LAN.
The WRT54G should now NOT use NAT, but act as a router.
The second subnet should have IP addresses 192.168.21.1 provided to the
WRT54G and having DHCP addresses allocated to its client. I want to use
packet filters to enfore this IP range and protect my LAN.

For connecting to the WLAN I want to use Radius (with WEP) pointing to
192.168.20.13. Is the Internet connection a limitation here?
Preferably I would want to force some people to use a specific IP addresses
in the range so I can make a distiction between 2 types of users with
different access rights on the LAN. What options can Radius provide to
support this?

Another option would be the LinkSys making a connection to a local VPN
server (Windows 2003 computer) and setting up the packet filter at this
location. The disadvantage is the increased load on this system, reducing
network performance for fast file transfers. It would be my second option.

What are my (un)possibilities with this suggested configuration or are there
suggestions on how to do it better?

- Joris