I did it, but I am not sure exactly how or why...
1. I first did a fresh install of SL, the myHack version to be specific.
2. I made three partitions, just as I did above.
3. After that completed, I did a fresh install of XP onto the first partition (after a quick-format of NTFS). This set the first partition as the active boot partition.
4. I rebooted with my install disk and, using Chameleon, at the prompt, handed the boot off into the SL load on my second partition.
5. I then changed my active partition from XP to SL. This took a few steps: First, I went into /System/Library/CoreServices/Directory Utility and 'Enable Root User' from the Edit Menu. Then I opened up a terminal window and did a fdisk -e /dev/rdisk0. This enabled me to view the partition table and then 'flag 2' to make SL the active boot partition. Saved that and quit terminal.
6. Modified my com.apple.Boot.plist files to include the standard:
<key>Default Partition</key>
<string>hd(0,1)</string>
Since I was not sure which would be used, I did this to both the /Extras and the /Library/Preferences/System Configurations files.
7. Rebooted, and all worked fine...
So, I am not sure what I did wrong to begin, but I think it helped that I loaded XP second and then flipped the active boot partition. Heck, I really dunno, but it works!
Hope this helps someone...
TE