if you have dd-wrt and want to use that as a wireless ethernet bridge on the 360 its easy. u don't have to use wmwifirouter unless you want.
Step 1 use wmwifirouter.
Step 2 go into your routers config webpage in ddwrt for wireles status "http://192.168.*.*/Status_Wireless.asp" replace stars with your 2 digit setup normally 1.1 or 0.1 enter your router password default for dd-wrt is root/admin click the site survey button ... then click join on the wmwifirouter signal.... wait for the config page to change to wireless settings and hit apply. wait about 30 seconds and whateve is connected to the ethernet ports of the router will be sharing the mogul internet connection. You won't be able to use wifi from the router to connect wireless devices as the wifi is connected directly to the mogul kind of a wireless Wan cable type connection.
Or you can go the totally free and better app in my opinion is ICS control v0.21
http://forum.xda-developers.com/showthread.php?t=377047
Dl and copy the ics control file to the storage card or install the cab file.
Step 1 go into settings > wifi > Menu > add new and create an ad-hoc(peer 2 peer) connection name it whatever you want to show up as.
save and exit.
Step 2 turn on wifi if not already on.
step 3 launch the ics control program set the first dropdown to cellular line and the second one to tnetw11(wifi)
step 4 set to auto connect to network with the check mark.
step 5 save settings bottom right. then click start (within the program)
step 6 is just like step 2 with wmwifirouter... the fist 4 steps only needs to be done the first time you do this to create the network so ics can broadcast the internet signal network you created. from that point on u can just launch ics and turn on wifi and should work easily it does not require config every time only if u want to change some settings. Uses tcp/ip stack to talk directly to the modem and will not requre the use of third party solutions