I asked this question before but no one seems to be answering my question. anyway here is what I wrote
I'm making a file server and the eth0 is acting up again with the same problem so I'll do all the steps. When I do ifconfig their is no line starting with eth0. all the rest are there the inet adress and the word UP. When lspci is done there is a line with sis900 in it. so after I did modprobe I got these error messeges. /lib/modules/2.4.20-8/kernel/drivers/net/sis900.0: ins mod/lib/modules/2.4.20-8/kernel/drivers/net/sis900.0 failed.
What should I do next?

try to install a lastest kernel version with lastest modules ...

also, you can try other modules : tulip, 8139too, etc..

I had many problems with this card with older kernels. It would work, then it wouldn't, it would work, then it wouldn't, blah! I finally got a 2.6 kernel on this machine and fixed it for good, it seems perfectly fine now.