Problem is, honestly, I'm pretty scared to even think of switching. There's a lot of lingo that seems so different; there's a totally different OS; there's that mouse with only one button.

Some things I don't understand are PCI-X and using 3rd Party (PC) parts and gear, as well as software, so I'll do this pointilized:
1. What the heck is PCI-X? Is it backward compatible with PCI cards? What can I do to get more PCI slots available in my Mac?
2. Can you use 3rd Party parts, like HDD's? I've noticed that there's already a post about using 3rd Party memory. Is there anything in a Mac that's totally propriatary?
3. Where do you buy software?!? I can go anywhere and buy PC stuff, get games at Wal-Mart, etc. I can't seem to see where Mac people get software at all, other than the Mac site.
4. Plug-ins - I see that FXpansion has a VST to Audiounits adapter. What other plug-ins are there for Mac? I'm looking at DP4.5, just to stick with MOTU stuff. (Ease of use and all that)
5. Is there any OS tweaking that you have to do to get up and running well with a Mac? (Doing Audio, of course)
6. Any caveats or things I should know before taking the plunge?
Any help would be appreciated. Thanks again.
Jean-Pierre