Recently, I've installed SimplyMepis as my distro of choice and have customized it far enough not to want to wipe it out and reinstall to fix a problem.

I've posted about this problem at the Mepis Lovers forums but got no response, and I'd like to get this fixed ASAP so I'll paste my post here:
"So on the first day that I installed SimplyMepis, everything was relatively fine and dandy in relation to my network. By default, eth0 and wlan0 were set to DHCP and boot at start time. Since I use a static IP network for my ADSL, it is no surprise that both of them failed to load and timed out. However, once I got into the actual OS, I could still run the pppoeconfig thing and it would recognize eth0 as ethernet and connect me to the internet.

When I started customizing my system, I decided to do to my eth0 connection the same thing that I did to my network adapter in Windows. That is, wishing that everything would start at boot without timing out, I set eth0 to static IP and put in the same stats that I used for XP. Clicking apply, and then trying to start eth0, it still failed. I then copied the stats from eth1, which still had the static IP numbers set by my pppoeconfig, and clicked apply; now eth0 loaded. Content with my work, I made sure eth0 was set to load at boot time and restarted my comp.

This is where the problems start.

I rebooted and the log screen informed me that ppppoe could not load eth0 because eth0 was not an ethernet device; thus, I lost my adsl connection. Once I logged into linux and ran ifconfig eth0, it indeed said that eth0 was UNSPEC, whereas eth1 (which I didn't change) was still ethernet. I couldn't connect through eth1, however, since there is no physical device for it.

Anyhow, I tried setting eth0 back to default settings by setting it to DHCP and rebooting. As expected, it failed to boot eth0 up but it still wasn't being recognized as ethernet.

This is essentially the gist of it; how do I make it become ethernet again?

On sporadic occasions, I got it to be ethernet again two times; first by doing something that I am not aware of (or perhaps nothing), the second by going into the SimplyMepis live CD and reinstalling the X config. After the first time, a simple reboot brought it back to UNSPEC status. After the second, I ran various updates, rebooted, and discovered that it again was no longer ethernet. Reinstalling the X config from the SimplyMepis CD now does no good (probably due to the updates)."

Now then, my computer has a 3com ethernet card and a firewire card. The reason I mention the firewire card is that there have apparently been problems with linux configuring the firewire card to eth0. I don't think this is the case for me here, however, because I was able to connect to the internet via eth0 even after setting up my firewire HD connection. In addition, if eth0 were given to firewire, then eth1 would become my ethernet connection. However, while linux does consider it to be ethernet (and has since install), whenever i run pppoeconfig, it says that eth1 has no "connection concentrator" (which I assume means no physical representative) and therefore cannot be configured for my ADSL connection. Similarly, I tried to configure RP-PPPOE to eth1 but every time i tried to initiate it with "adsl-start" it would time out. In result, I think that the problem here is with linux incorrectly classifying my ethernet card.

Also, whenever I run the live CD, it detects eth0 just fine.

I would really like to get this problem fixed.

I've a new development. I disconnected my 3com ethernet card and booted into Mepis and looked into the network choices. Eth0 was still there but eth1 disappeared, implying that it considers eth1 to be the network card and eth0 to be the firewire card (or perhaps something else?). So, this would be all fine and good if I could connect through eth1, but I can't. Pppd doesn't allow me to configure it for eth1. Rp-pppoe, on the other hand, does connect, but it is a fake connection because I can't surf the web, use gaim or anything else that uses the internet. So it might as well not have connected.

Any ideas?

The 'fake connection' could be a starting point - it perhaps means that you're connected, but DNS isn't working. If you could post the output of '/sbin/ifconfig -a', then maybe someone could help.