I've been RTFMing and cruising the forums but haven't been able to figure this one out.
In 10.1 I reinstalled zmd, rug, zen and the required dependency's [I had removed them as well as beagle and nfs to increase performance which it did]. When I rebooted I get 'Error 15: File not found'. How can i correct this??? Also when I get an error with a number where do I find what the number means???

Error 15 is a grub problem that basically it can't find the kernel. Either the partition numbers changed (like if you broke up a partition into two partitions ahead of it) or you removed a kernel or you edited the menu.lst and made a typo. Not sure if any of those sound right.

You should be able to recover from this. Here's a link that might help (as I'm a little weak on grub). It tells you step by step what to find your proper kernel and boot it.

I've made some progress. I went into Yast>System>Boot Loader and edited the problem partition [Old Suse] thus:

Under Kernel I changed it from:
[hd0,1]/boot/vmlinuz
to
/boot/vmlinuz

and under Initial RAM Disk from
[hd0,1]/boot/initrd
to
/boot/initrd

and now Grub starts booting into /dev/hda2 [Old Suse] so the boot problem appears to be corrected partially. Now while it's trying to boot into Old Suse 10.1 I get this error:

Modprobe: Fatal: Could not load /lib/modules/2.6.16.13-4-default /modules.dep: no such file or directory.

When I use rescue CD I run:

#mkdir /mnt/suse
#mount /dev/hda2

and that works. Is there anything I can do at this point to fix the problem?

Next I run:

chroot /mnt/suse

and get this error:

Fatal: Kernel to old

I think what might have happened is by removing [hd0,1] you pointed the boot path to the NEW kernel and initrd. These should fail to load because the Old Suse won't have modules built for the new kernel. You need to point it to the kernel installed in (hd0,1)/boot (which is /dev/hda2). Does that make sense to you?

Yes it does make sense but when I config that way Grub gives me 'Error 15: File not found Press any key to continue' which I do and can boot into any of 3 OS's as I'll describe.
Ok, I have a multiboot box with FC5, Kubuntu Dapper, Old Suse [/dev/hda2] which was 10.0 upgraded to 10.1 which has a lot of data I'd prefer not to lose but can't boot into currently, and a fresh install I call New Suse [/dev/hda7] which I installed 2 days ago on the unused partition. I currently have a boot config which will start to boot into /dev/hda2 and does load some things but stops at 'Starting Service xdm' and gives me the error:

Modprobe: Fatal: Could not load /lib/modules/2.6.16.13-4-default/modules.dep: no such file or directory

during the boot process this message was repeated many times but the process freezes at the point I described.

What is the kernel in /boot on /dev/hda2 and what folders are in /lib/modules of /dev/hda2? Maybe you can find a kernel, initrd, and set of modules that all match up??? Sorry, I'm struggling a bit with this one too.

Can you just move the data you want to keep to the new Suse by mounting the old partition from the new install?

I can't get into /dev/hda2 with failsafe, System Rescue CD, or Install CD. I can't get /dev/hda2 to upgrade with Install CD. Is there another way I can access files in /dev/hda2? Like maybe with a virtual console?

Actually I was able to save my old Suse partition by running an upgrade with the Suse 10.1 install CD's [thereby actually downgrading from 10.1 to 10.0]. For me Suse 10.0 is more stable and faster than Suse 10.1 although I have 10.1 on another partition to play with.