It might be the limitation of the existing kernel and that is why it is not able to detect the ethernet card. You can try building the custom kernel using the following steps:
1. Get the kernel from www.kernel.org
2. Usually it get downloaded to /user/Desktop location.
3. Copy it to the location where you have enough space.
3. If it is a .bz file use tar -xjvf file_name else go with tar -zxvf file_name.
4. Once the above file is extracted go in the extracted directory and check if you see any .config file
5. If not the next step is to run make config or make menu config or make gconfig or make xconfig depend which tool you want to use to create custom kernel. I prefer using make gconfig.
6. Once the tool is launched you can select which options you want there in the custom kernel. Make sure that your custom kernel is modular so that you can load device drivers as module instead of compiling them with kernel. This also enhances performance.
7. Once done with building up the configuration save it and exit the tool. This will create .config file in that location which will contain custom settings that you did with the tool (make config or make menuconfig etc)
8. Run make mrproper
9. Go to the file with the name MakeFile which will be in the same location as that of extraction. Change the EXTRAVERSION parameter in that file to the name that you would like to give to your custom kernel, save and exit. Do not change anything else.
10. Now before going with make rpm. Make sure that you have enough space on /usr directory. If you have anything important there then copy it to some other location. For me it worked even with 2 GB. But you can go with a little more say 3-4 GB.
11. Run the make rpm from the location where you have .config file.
12. After running the above command you will find the rpm in usr/src/RPMS/i386 if you have built it for i386 architecture else look under the appropriate architecture directory under /usr/src/RPMS
13. Run rpm -ivh rpm_filename (Do not run rpm -Uvh as this will upgrade your existing kernel and what if this new kernel didn't work for you)
14. After installing the new kernel make appropriate changes in /boot/grub/grub.conf file to reflect the new kernel load script.
15. Make initial RAM disk image for your new kernel. This you can do by going in /boot directory and then issuing makeinitrd /xyzkernel.img kernel_name. Where xyz will be the name of your custom kernel.
16. Reboot the system and see you see a new kernel entry at the startup in grub :-) If you find any issues with new kernel then we can always boot in old kernel to get it fixed :-)
If you are planning to perform a fresh install then at the boot prompt where it ask you to select the way you want to install go with linux noprobe this will prompt you to select every driver according to your wish (Ofcourse you need to know which driver will be required for your device)