On another Slackware 10.1 box I tried replacing the network card that was in there with some better ones I have. None of them worked just plugging them in. So now I've got the old one back in, but I can't get it working. lspci shows my network card, but netconfig doesn't properly configure it. What can I do?

post the results of "ifconfig eth0"
try this if eth0 is there...."ifconfig eth0 up"

eth0: error fetching interface information: Device not found!

Look at the card it says at lspci and search on the web which module should be loaded so Linux can recognize it. Load the module and run netconfig again.

If that works, add the line to load the module in /etc/rc.modules so it will be loaded each boot.

first off post the make and model of ur NIC
ill help you look for a driver, if its linksys then its more than likely gonna be tulip

Haven't searched the Web for a module yet, but here's what lspci says about my Ethernet card:

00:0b.0 Ethernet controller: Winbond Electronics Corp W89C940

BTW, I'm using the 2.6.10 kernel from the "testing" packages on the Slackware CDs.

I think you have to compile ne2k-pci module from your 2.6.10 kernel tree

Did you install kernel-source 2.6.10 package ?

Yes, I did install the kernel-source-2.6.10 packages.
How do I compile this module? Do I have to go through and reconfig and recompile the kernel?

No just the module I think,
copy the config file for kernel 2.6.10 (it is surelly in /boot)
in /usr/src/linux, rename it .config
then in /usr/src/linux :
make menuconfig

go to :
Device Drivers / Networking support/
Network device support / Ethernet (10 or 100Mbit)
Tulip family network device support (enable it if disabled)

Then, add Winbond W89c840 Ethernet support if you have it

[edit]
To compile it as module, mark the corresponding checkbox with a <M>

Also after that, make modules && make modules_install

[edit2]
Or you could choose to compile and install the driver from :
http://www.scyld.com/ethercard_drivers.html

Thanks keefaz!
I'm going to try recompiling the kernel, though, with built-in support for my Ethernet card rather than modular support.

Do not forget to run lilo after kernel install, in this case

Yay - it works! Thanks guys!