FreeBSD 5.x source update and compilation problem in HP Vectra VE18

[Ganbold]

Hi,

I installed FreeBSD 5.1 in HP Vectra VE18 PIII 450MHz with 128MB RAM and 
4GB HDD.
However I'm having problem compiling sources. Whenever I try to make buildworld
make stops sometime later saying some variable not found etc. When I check 
that variable from source
it is somehow changed strangely something like: addend changed to adddnd, 
else changed to dlse, INFOPATH
changed to INFNPATH etc. I did cvsup several times, also I used

rm -rf /usr/obj
cd /usr/src && make cleandir

command before compiling. I don't know what to do, I really need to install 
FreeBSD 5.x on this machine.
I even tried with FreeBSD 5.2RC2, but same results. Also I first tried to 
compile kernel , but it is same, no results.
Can somebody help me in this regard? What should I do?

tia,
Ganbold