I have a cheap Trendnet adapter which works well under Kubuntu 11.04 on my 9
year old iBuddie laptop. One thing I found was not to use wicd (the
replacement wifi client). It wouldn't connect at all. Also, I had to plug it
into the computer directly as even a USB extension that came with another
wifi adapter prevented it from connecting.

If you can connect under Ubuntu what would happen if you installed Ubuntu
and then added kubuntu-desktop from the repositories? Might work, even
though it's a bit cumbersome.

If it works in Ubuntu then it should work in Kubuntu or Xubuntu or any
other *ubuntu you can find

Try connecting the Kubuntu / Xubuntu systems using an ethernet cable
then getting updates. That often brings USB Wi-Fi adapters to life so
always worth doing first.