i have Slackware and am currently trying to setup a second network card, right now i have an isa card working(NE2000 i think) and i am trying to get this card i got to work(it is a PCI card).

when i boot it gets my isa card and configures it right as "eth0", but my new card gets configured as a loopback and is called "lo"

i have edited the file /etc/rc.d/rc.inet file but that don't help, but i have tried executing it after bootup and that makes both network cards, but when i run it it says "SIOCADDRT: File exists" both before and after it says

Configureing eth0:
ifconfig blah
Configureing eth0:
ifconfig blah

but then when i run ifconfig it says i have eth0(my isa card), eth1(my new PCI card), and lo(the thing that appeared as the second card after boot, and still in loopback)

so what do i do to get both cards working at bootup

You are missing an important step. Each network card has an associated driver, and you specify this /etc/modules.conf. You'll find some entry like
alias eth0 <some name>
in my case
alias eth0 3c59x
so that tells the kernel to load that module whenever the eth0 interface is activated.

Find out which driver is the one for your new card, and add
alias eth1 <that driver>

you can either reboot, or do a depmod -a to get it. The rc.init has little to do with it, you need to use some GUI to configure eth1 or just make the config files.

After that depmod -a, you should be able to get a response to ifconfig eth1.

If you don't know what driver to use, do lspci and see what card and chipset it is, that will give you a clue.

Hope it helps,
mlp