Confused you will be!
I've got a load of PCs I can run Windows on so I'm not at all fussed if any Mac I buy can't run Windows and was trying to avoid any helpful posters suggesting I buy an Intel based Mac so I get the best of both worlds.
I'm not sure what ver 10.5 (which If I understand correctly needs a newer, more expensive, mac) offers over 10.4 and how much that matters. My present impression is that about once a year Apple brings out a point release of OS X with a few new toys and that their fanatical customer base slings them the best part of hundred quid each to make sure that nobody sneers at them.
I'd be the last to be an apologist for Microsoft, having using Windows since the dreadful Windows-386 back in 1988 (when it was bundled with Aldus Pagemaker and Microsoft Excel) but this behaviour is at odds with that of many Windows users who frequently need a lot of convincing to take up new versions of Windows, as can be seen with the slow take up of Vista. Windows-XP, which I've been using since 2002, is reliable enough, the upgrades have been free, and I've not been forced to buy a new OS. I'm not sure if this is the case with OS X and whether the later releases fix a set of bugs or just provide more shiny toys?