Hi
Can you state a bit clearer what your configuration is?
The way I interpret you post is that your PC is connected by ethernet cable to an ADSL modem or router. If this is the case then configure your modem/router with the ppoe settings BUT configure Mandriva internet access to Ethernet access - Mandriva does not need to know about ppoe - only that eth1 is where to look for DNS etc. If your modem/router provides DHCP, then you can configure this in Mandriva as well.
Its only if your PC is connected by USB to an ADSL modem that you need to configure ppoe internet access within Mandriva.
Hope this helps.