I has installed Fedora 10 on a 2 ethernet computer. I need that the ethernet detected as eth1 be eth0.
I deleted all the network cards on the network manager then turn off the computer. Then removed the network card that was detected as eth0 and rebooted. Added a network card on network manager and it is set as eth1 again but it is he only ethernet card on the computer. Where do i erase all previous detected ethernet cards so it will not remmenber them?

The files are in /etc/sysconfig/network-scripts. They are in the form of "ifcfg-<dev>" e.g. ifcfg-eth0, ifcfg-eth1.

You want to make sure this directory has only a single ifcfg file for each device. Some people make copies and those are seen on start up and confuse things.

The ifcfg file should have the MAC Address of the specific NIC. You ought to be able to make eth1 eth0 simply by copying ifcfg-eth1 over ifcfg-eth0 then edit the file to insure it calls itself eth0 rather than eth1. Then run "service network restart".

Be sure you save all the ifcfg-<dev> files to an alternate location before you change anything. If it doesn't work you can put them back and restart to get back where you started.

What about /etc/udev/rules.d/70-persistent-net.rules. Should it change it there too.
I ran a find for the occurrence of the mac number of the network card and found it on this file.

OK that's a new one. Looking at an F10 system here I see it ties device name (eth0, eth1 etc) to specific MAC addresses. Given that you should definitely update the rules file. (Save a copy to /root first.) Make sure the MAC address matches the interface (e.g. the line that has eth0 make sure it has the same MAC address as what you what to be eth0 in the ifcfg-eth0).