I used the RC3 to boot the 10.6.2 without issue.
After formating one of my partition from NTFS to Mac OS extended (Journaled), I ran into can't find mach_kernel issue. I tried to reinstall RC3, replace new mach_kernel. Finally, I decided to reformat the data partition back to NTFS. After that, my 10.6.2 boot into 10.6.2 without any issue.
BTW: I tried to add the following item into the /Extra/com.apple.Boot.plist