when i ran the last test plugging the adaptor straight into the phone line, skipping the DSL filter, i didn't wait long enough. I just tried it again and it works.

It seems you're righ that the DSL filter is causing a problem with the phone line card.

BTW - i'm using the DIAMOND HomeFree Phoneline Network USB card.

http://www.overstock.com/cgi-bin/d2.cgi?cid=48418&PAGE=PRODUCT&PROD_ID=26714&fp=F