[CentOS] missing module dir?

I'm teaching myself about ethernet cards, and found a TLDP page. I have 
CentOS 5.3.

In this section:    http://tldp.org/HOWTO/Ethernet-HOWTO-2.html#ss2.4
in the 'Driver as module' subsection, regarding PCI cards, it states 
that there should be a directory   "/lib/modules/`uname -r`/net"

[mykolas at sr1220 ~]$ uname -r
2.6.18-128.1.16.el5
[mykolas at sr1220 2.6.18-128.1.16.el5]$ pwd
/lib/modules/2.6.18-128.1.16.el5
[mykolas at sr1220 2.6.18-128.1.16.el5]$ ls
build   modules.alias   modules.ieee1394map  modules.ofmap 
modules.symbols  updates
extra   modules.ccwmap  modules.inputmap     modules.pcimap 
modules.usbmap   weak-updates
kernel  modules.dep     modules.isapnpmap    modules.seriomap  source

There's no 'net' directory. I am guessing that the NIC drivers are 
modules (and not compiled into the kernel) - am I wrong? Or, where are 
the modules?