As far as I know it depends more on the card you use. I have an Asus card that does support WPA. With wpa_supplicant, which is part of the cacko rom, and several others, it works. I even have eduroam working. That took quite a bit of fiddling though. But in the end it turned out to be quite simple.
So, it is not the Zaurus that is the bottleneck, but the wlan card and rom you are using. Check the specs of your card and search the forum for wpa_supplicant and you'll find the info.
BTW, I have an sl-c3100 like you do ;-)
MaBo