Yes - Ive seen that too (may have been for the 120 only) on the UK draytek website FAQ section (can't access it now thanks to xnet's international meltdown)
On my 100 there is no option to disable the PPPoE Client...I'll try to dig up a screencap. FWIW I'm using the latest 2.7.3 firmware from the UK draytek site.
[EDIT] Here's the setup guide from draytek UK: http://www.draytek.co.uk/support/kb_vigor100_setup.html.
SWEET! On re-reading the setup guide it says this:
An important item to note is that for the PPPoE connection a "Service Name" should never be entered. If you have this field in the configuration of the router or computer that you're using then make sure that it is left empty.
On removing 'xnet' from the service name of the PPPoE setup on Tomato it's all working as advertised - Ahhhhhhhhh!!
[SOLVED - and thread back on topic - apologies for the hijak]