5.1-RELEASE install giving me random errors

[freebsd]

I finally managed to get the first disc of 5.1-RELEASE downloaded and verified
the md5 hash for it.  I burned the image to a cd and rebooted.  I then
remembered that my computer for some unknown reason refuses to boot FreeBSD
cds (doesn't matter which version, yet it has no problem booting my win2k cd).
 So, I make the kernel/root floppies and reboot again.  I decide to do a
network install.  Everything goes fine, and I reboot to my fresh install.

The first thing I do when installing FreeBSD, is configure make.conf and
rebuild my kernel/world.  I start the buildworld in one terminal, and start
configuring the rest of the system while that is going.  Every so often, I
check back on the progress.  After a while, I see some strange error (I don't
have the exact message, and I'll explain why later).  I figure I'll fire up
windows to search the mailing lists.  No one else reporting this error
message, so I tinker with a few things on my end.  Nothing I do will make the
world build.  I finally decide that I will just re-install it from the cd this
time.

I boot from the floppies, and when sysinstall asks where I'll be installing
from, I point it to my cdrom with the cd in it.  It promptly gives me an error
message about not being able to locate /dist.  I move the cd between my
drives, and no luck.  I decide to try another FTP install, but this time from
a different mirror.  Once again, the install goes smoothly, and I reboot.

This time when I try to build the world, it runs happily for about 50 minutes
(where as before it died after roughly 20 minutes).  After that, it errors out
processing expr.c, complaining about a lot of undefined variables and other
fun stuff.  Once again, I try playing with some settings on my computer
(namely removing compiler optimizations from make.conf), searching mailing
lists, etc, and once again it seems I'm the ONLY person having problems with
this release.

Also, when trying to build cvsup so that I can make sure my sources are in
sync, ezm3 fails building at RealLong.i3.  CPU usage climbs to 100% just
before the build segfaults.  This has never happened to me on 4.8 or
5.0-RELEASE, so I'm baffled.

What am I missing here?  Heat is not an issue (only gets to about 50C after
hours of gaming, which is actually cool for this computer).  The hard drive is
new within about a month, so I SERIOUSLY hope that nothing is wrong there. 
The memory is some nice Corsair, recently purchased.

My system specs:
Athlon 1.2ghz
768mb PC133 SDRAM
200 gig Western Digital hard drive
BIOS only supports up to 137 gig, so also using a Promise Ultra100TX2
controller card

Any help would be most appreciated.