Make sure you use an 0S 10.5 RETAIL install DVD disc.! I now have had 3 sets of grey dedicated disks not work 1 Retail 10.5.2 UPGRADE disk did not upgrade 10.4 to 10.5 BEWARE!
MacPostFacto people are working on a hack to run at least Mavericks on 2006-2007 Macs. So far they have it working on 2007 Mac Pros. But iMacs and MacBooks will come later, if at all J.C.