As with all things, you have to match the hardware to the software. Yes, Vista is a resource hog, but so was every single prior revision of Windows when it shipped. Win95 requires 16MB RAM? WTF? Where will I ever get that much?!?
The Mac is no different, the latest and greatest features require up to date hardware to work efficiently.
I paid $1100 (plus tax) for a dual core laptop with 4GB RAM, 320GB HDD (and room for another that can be set up in a RAID configuration), a 17 inch LCD with a built-in webcam, and an Nvidia 8800 graphics card with 512MB RAM. Yeah, it is a laptop and it runs Vista 64 like a dream. Exactly what kind of Mac will I get for that price? A bottom of the line MacBook with barely a GIG of RAM, whoopie!
If you can’t afford $1100 bucks then stick with your old hardware and software, or run Linux and put up with driver incompatibilities, fiddling with repository conflicts, and shoddy support. Enjoy your user support experience there!