Now I wonder why this is happening, then I remember that I had just recently compiled a new kernel and I had this problem on a machine sometime ago where sometimes certain kernel versions would assign eth0 to my wireless and eth1 to my wired and other versions would get it backwards. This seems like a flaky thing for the kernel o do, but it is actually assigning the names to the cards in the order that it sees them. If the wireless card responds to a probe faster than the wired card, it'll get eth0. If it's the other way around, your wired card will get eth0. The good news is that there is a way to prevent ever having to deal with this issue... a little service called "ifrename". To install ifrename search for it in your distro's package manager, or using apt on Debian based distros use

apt-get install ifrename

Now you'll need to find out the MAC addresses of all of your network cards. A MAC address is a globally unique identifier that every network card ever manufactured has. Use the command

ifconfig

and look through the output for each card (eth0, eth1, etc..) for "HWaddr" followed by a grouping of 6 sets of hexadecimal numbers separated by colons (eg. ab:cd:ef:01:02:03). Now open edit a file called "/etc/iftab" and put lines in it for every network card in your machine with the following format. [name] mac [actual mac address]. Here is what my "/etc/iftab looks like (with the actual MAC addresses not shown for my own security).

wired mac 00:00:00:00:00:00
wireless mac 00:00:00:00:00:00

Now you just need to edit your "/etc/network/interfaces" file and make the appropriate changes from "eth0" etc.. to "wired" etc.. Now just restart the ifrename service with the following command

/etc/init.d/ifrename restart

and now your network cards are named like you want them and they'll always be named right no matter which order the kernel recognizes them in. Now instead of "ifup eth0" you use "ifup wired" and such.