Is there a way to install 10.3 without reinstalling grub on my box?
I already have a grub boot partition that I boot some other OSs from and when I install 10.3 and let it reinstall grub it screws everything up.
Now I have removed Suse and fixed my grub and want to reinstall Suse 10.3 and just manually edit my existing menu.lst.

Sure. Change to the Expert pane during the proposal and change the Boot Loader location to your OpenSUSE root partition. You'll need to boot into your other distro at first reboot to add the OpenSUSE Kernel lines into a new OpenSUSE section of your normal Grub. Then you can use your grub to boot into the rest of the installation, which takes place from a hard drive boot into the OpenSUSE system.

I've never done this, and I'm pretty certain this is part of a document on opensuse.org's documentation or SDB wiki pages. There's likely a complete document there for you to print out and have by your side with all the details. So look around there before going ahead.

I'm unclear because I've never had to do this for myself, but it isn't unusual. The SUSE Grub can also be configured to boot your other operating systems just like yours can if installed normally into the mbr, replacing the other one.

Either way works as long as its sections are configured with the correct stuff in there to boot whichever Kernel it needs.

Thanks!
I'll give it a shot when I get ready to try out 10.3 again.