From what I read these adapters worked fine in Ubuntu 6.0 but not
since then :-( Also read that adapters based on the Prolific
PL-2303 chipset work well with Ubuntu so perhaps a change of hardware
is indicated ?

http://www.cooldrives.com/usbtoserial.html looks a good place to
start.

B> I am using Aitlink 101 AC-USBS USB to serial adapters.