Im using, or atleast trying to configure my pppoe to access the internet via my windows laptop, because the modem I have, according to the folks at linmodems.org, does not have 64bit support, and probably never will have, since the folks that manufacture my modem are not willing to release thier source code so that linux developers can compile drivers needed for its operation. As you will recall, I have a usb modem, which also doesnt have driver support, and is thus unavailable to use under linux. Also, with my Acer being only a couple of months old, it does not have a serial port that I may try connecting a serial modem to, so that option is also unavailable to me.
To connect via your Windows machine, the only thing you should need to do is turn on 'connection sharing' on the windows machine. The Ubuntu machine will detect and use that connection automatically (via the magic of DHCP)
I will install Samba on my Acer Linux desktop, and have already enabled sharing on my folders on my Windows Vista laptop, however, the problem that I have is that under Heron, I cannot get my pppoe settings to 'stick' as it were, as soon as I click on them, they deselect themselves and uncheck the pppoe box. This is what I am trying to investigate the cause of.
Simple answer 'because there's nothing to connect to'. pppoe is used to connect to the net via a specific type of ADSL router that bridges pppoe to pppoa. Even then, the vast majority of ADSL routers do the pppoa negotiation themselves and simply provide a plain IP connection. If you're not using ADSL then pppoe is something you almost certainly don't need and have no use for.