Dual boot works now, I'm in Mageia atm but also have f18 on board. Both work pretty good on this older hardware.
The issue was indeed LVM. The only difference this time was that I used standard partitions for fedora. I did have problems with the fedora partitioner, it would get to a point where it reported 50 GB free space but when I tried to set this to /home it said there was no space on the disk. I had to restart the installer to get through this, but ultimately I booted Mageia and used diskdrake to set the partitions. Then in the fedora installer I just used "reclaim space" on them by selecting mount points and checking the "format" button.
Note that the partitioner will not make the changes in mount points until you select the format option.
There is no place to change the boot loader behavior as far as I can see. It installed grub2 and added Mageia to the menu.lst. In other words it's using fedora's boot loader, which is what was recommended in all the forums I looked through trying to figure this out.
With these 2 systems on here I have everything I could ever need, not the least of which being a mobile platform for evangelizing about Linux in general and Mageia in particular.

I'm a happy camper, a big thanks to both the fedora and the Mageia teams.
Just like Mandrake back in the day, it just takes a couple trial and error whacks at it and you'll know your way through this new fedora installer. I'm going to keep testing fedora, so I'll keep my eyes peeled for any options with boot loader settings...