i picked up one of these used. actually helped someone else get one working last summer (which was interesting). they are not 'easy' to configure. just a couple of blinky leds to let you know status. i knew what to expect...
I was pretty frustrated setting this up, mostly because i got my own wep key wrong. um. oops. the issue here being the device or manual doesn't explain what the status lights mean. (Activity light blinks slow when wireless/lan is active, blinks faster when properly connected to AP). the device is pretty straightforward, assuming ya don't screw up something like your own wep key! something keep in mind: i always enter mine using hex codes for each character (avoids confusion between vendors).
if you follow the manual you know the first part. the trick to configuring the device is to make sure your laptop is on the same subnet (dwl-g820 is set for 192.168.0.35). i just set mine to 192.168.0.1. (no conflicts here since my AP uses a different subnet). then just use the device's admin web pages (http://192.168.0.35) to configure settings to match your wireless AP --nothing fancy here. note: you do *not* need to set gateway or DNS settings here, just IP and subnet mask.
once you set the AP settings (SSID, channel, wep key, et al), change your laptop to use DHCP (if your AP is set for that). that's it --it should work right from here with no other changes. dwl-g820 will route the DHCP request to the AP, and the laptop will grab a new IP from your AP. period.
switching back and forth was simple and didn't require a reset anywhere (as i previously assumed). simply set your IP manually so you can reach 192.168.0.35 for configuration, or DHCP for normal connection (will get IP directly from the AP, assuming the AP is set DHCP). if properly configured, the dwl-g820 will automatically route packets in either case. the manual doesn't explain much here since in theory, there isn't any more to do. almost too simple?
really, a text status readout on the device would have helped a lot here (but would have added to cost). also, i'm not sure this device will associate with any random open network out there automagically; you need to manually change your settings anytime the network changes. assuming you have a laptop connected (my scenario), doesn't take long to change settings at all once you get the hang of it.
note: as far as i know, the dwl-g820 will work with any 802.11b or 802.11g access point.
question: is there a conflict if you have your AP set on the same subnet? haven't tested that. wonder if people are having issues with that.