I'm using Xubuntu 6.06 on an IBM TP 600E laptop.
I've got a 3com 3CRWE254G7 (according to lsusb) USB adaptor, and a Linksys WPC54G v5 (Marvell 88w8335 firmware according to lspci) PCMCIA adaptor.

I've installed both of them with ndiswrapper v 1.8 (utils version 1.7 apparently) which I got through apt, using both the drivers on the CDs and the latest ones from the manufactuers.

I can only connect to WPA-encrypted networks, but want to be able to connect to unsecured ones, too.

The Linksys one connects fine to WPA-encrypted networks. I've not found a WPA network to try the 3com one out on yet. Both do unsecured networks with WinXP.

I've tried the default network-admin, and i've installed wifi-radar, but both have the same problem - DHCP requests time out (there's definitely a working DHCP server - everyone else can connect). Same thing happens when I do it through xterm. Wifi-radar's measure of signal strength is incredibly fluid, but that could well be accurate.

Any ideas what's causing this and how I can fix it?

All I can find are other people with this problem, but no-one with a solution.