I am seeing the same issue:

On my OBSD machine:
Using disk 1 on the openBSD 4.1 distro, it boots like a champ.
Using disk 1 on the OpenBSD 4.2 distro, it skips the cd and goes on to the 
next step.  By Skip, my "guess" is that it doesnt find an appropriate 
bootblock on the cd to boot from, and then goes to the next device in the 
boot order.

I even went so far as to try different positions in the IDE chain for the 
cd drive (secondary/slave, primary/master, but no difference).  I also 
tried disabling all other bootable devices in bios and leaving only the 
CD-rom as a viable boot device, and it still would not boot.

My solution was to burn cd42.iso to a cd and boot off of that.  That 
worked well for me.

Motherboard:
tyan trinity I845e bios rev:v1.10
As found here: http://www.tyan.com/archive/products/html/trinityi845e.html

Answers to other questions:
- The 4.2 cd does boot sucessfully on another machine.
- I didnt move the CD-rom drive to another machine, but it seems ok, 
considering it boots 4.1.
- cd42.iso does boot.
- I did not see a emu or install iso on the 4.2 disk 1.  (Find reveals 
only cd42.iso)

Hope that helps
--C
p.s. I'll send my dmesg over as well.


  On Sun, 28 Oct 2007, Nick Holland wrote:

quoted text
> This thread is a bit bothersome for a lot of reasons.  However, there
> is a lack of hard info so far.
>
> When you say it isn't booting the CD, what does this mean?  Does it try
> but fail with some error?  Does it not even stop at the CD on the way
> to attempting to boot the hard disk?
>
>
> And let's see what the actual scope of the problem is:
>
> Does the official CD boot?  (I think the point of this thread
> is for some people, no it doesn't).
>
> Does a copy of the official CD boot?  (Is there any error reported
> when trying to make a copy?)
>
> For the people that say the official CD doesn't boot, do they have other
> machines they /can/ boot the official CD?
>
> If people are spotting some machines that do and some that don't, what
> happens if you move the CD drive from one that does boot to one that
> doesn't?  Does the problem follow the machine or the drive?
>
> Does a CD made from install42.iso boot?
>
> Does a CD made from cd42.iso boot?
>
> Does a CD made from cdemu42.iso boot?
>
>
> If install42.iso or cd42.iso boot, don't be looking for code changes,
> sounds like we had a bum pressing of CDs or some other "quirk" in the
> way the master was made, as they all use the same boot process.  Still
> needs to be identified and fixed for 4.3, but it wouldn't be a code
> problem.
>
> Nick.