[CentOS] can't "make"

Hello.
I just fresh-installed 5.3 onto my laptop, and I have a problem trying
to get wifi working. Be aware that I have 5.2 on it, and did the same
process, and it worked great!

I'm using http://wiki.centos.org/HowTos/Laptops/WirelessAR5007EG  -- as 
I did for 5.2. The problem arises in section 6:

[mpk at a3680 madwifi-hal-0.10.5.6-r3968-20090402]$ make
/bin/sh: line 0: cd: /lib/modules/2.6.18-128.el5/build: No such file or 
directory
Makefile.inc:66: *** /lib/modules/2.6.18-128.el5/build is missing,
please set KERNELPATH.  Stop.
[mpk at a3680 madwifi-hal-0.10.5.6-r3968-20090402]$ ls
ath       BuildCaps.inc  hal      kernelversion.c  Makefile.kernel
README      release.h  THANKS
ath_hal   contrib        include  Makefile         net80211
README.dfs  scripts    tools
ath_rate  COPYRIGHT      INSTALL  Makefile.inc     patch-kernel
regression  SNAPSHOT

Q: 'make' can be run as $ - correct?

In another terminal:
[root at a3680 tmp]# whatprovides build
-bash: whatprovides: command not found
[root at a3680 tmp]# rpm -q gcc gcc-c++ make kernel-devel
gcc-4.1.2-44.el5
gcc-c++-4.1.2-44.el5
make-3.81-3.el5
kernel-devel-2.6.18-128.1.6.el5

I haven't a clue what's going on here, or how to fix it. Google's linux 
SE couldn't find any hits.