This document contains instructions on installing Linux driver
and adjusting speed for the series of RTL8139(A/B/C/8130) Network Adapter

Installing Driver:
(1.) Kernel Had Supported Driver:
Check the directory " /lib/modules/¡K./net " if you could find "rtl8139.o"
Your kernel had supported RTL8139 series. You could easy use "linuxconf" 
to setup your card. If you don't like linuxconf, you also could use
"modprobe rtl8139" and "ifconfig up eth0" to load module.
If your driver load properly, your "/etc/conf.modules" should include
line of "alias eth0 rtl8139".

(2.) Kernel Don't Support Driver:
If your kernel doesn't support RTL8139 series, you should compiler driver
by yourself. Please contact http://www.scyld.com/network/rtl8139.html
to get source code. The compiler command is located on the end of source
code. Maybe like "gcc -DMODULE -Wall -Wstrict-prototypes -O6 -c rtl8139.c".
If you couldn't compiler success, maybe you should refer to error message
and copy library or head file to Linux.

Adjust Speed:
(1.) Adjusting speed:
Driver is designed with the gold that no options should be needed in most
environment. However not all cards and networks can be automatically configured,
thus allow operational parameters to be modify when they are loaded
as module. Typically the following variables may be set:
insmod rtl8139 options=0x40
Hex Decimal Meaning
0x10 16 ¡K..Force Full-Duplex operation (must be used with 0x20 or 0x40)
0x20 32 ¡K..Force 100mbps-only operation
0x40 64 ¡K..Force 10mbps-only

If loading as a module and configured /etc/conf.modules

alias eth0 rtl8139
options options=0x40

Look weird like that but I believe that works.

That's what I got out of the documentation. It seems like the
options are supported in the module. If not, you'll need to
download ftp://ftp.scyld.com/pub/diag/rtl8139-diag.c

Compiling syntax is at the end.

Run: "rtl8139-diag -F 10baseT-HD"

That will force it to 10Mbps at half-duplex. If you want full-duplex change it to 10baseT-FD.
You'll need a switch for full-duplex.

Once you establish that it works, you can write the setting to
the EEPROM with "rtl8139-diag -w".

Other information:
You could get some helpful information on these URLs.

http://www.scyld.com/

http://www.deja.com/usenet

http://www.realtek.com.tw/cn/html

If you have any questions, please don't hesitate contact Realtek
Technical Support Team at cnfae@realtek.com.tw