Mepis has some really good built-in gui tools for network configuration. If you can post the output of
lspci | grep -i net
as well as
that will help.
You might check this
There really was a huge improvement from 6.0 to 6.5 in Mepis, and the beta for 7.0 is available, too. You might consider installing a newer version. It is my understanding that 7.0 (using the 2.6.22? kernel?) may resolve some previously unsupported hardware issues.
Post back and let us know how it goes.