Suppose you wanted to run several OS's in Virtualbox but you are wary of having all those large .iso files hogging up disk space, though liking the live-CD concept you rather have access also to your main OS while running the guest OS. Virtualbox allows you to run the .iso from off the CD instead of from off the hard drive. If you copy all those .iso files onto a DVD you can satisfy all the above requirements. The live-CD normally boots to takeover the computer, but in Virtualbox it runs as if it were another application on your main system.You could put a whole bunch of these .iso files on a DVD. And yes, the guest OS has access to network and internet I/O through the host OS. Since MS windows doesn't come as a .iso file, I don't think it can be burned to a bootable CD or DVD, but don't quote me on that. Run Mac OSX on Linux? That I know nothing about.
The main things I suggest to all you folks who hang onto older computers (you have your reasons), is that technology advances at the expense of the older technology. "It still works" is no longer a valid reason to keep it. Not only do companies no longer support those things, but the user base moves on to new products also. This means the knowledge of those things wanes and disappears. So, if your hardware is 5 years old or more, consider newer stuff or at least serious upgrading. Todays software requires more efficient CPU's and ample memory. The rule of thumb is to buy as much as you can afford first off, the tendency is not to upgrade unless you are forced to. Even if you get a good middle of the road processor, get 1 or 2 gig of memory. Vista requires 2 gig for good performance, Linux will run well in 512mb but the more the better, especially if you plan to do desktop effects or virtual machine. With memory, more is better.
Another thing to realize is what comes with the computer, I'm talking about wired or wireless.
Desktop users usually get wired but a great, great number of folk only consider laptops. Wireless connections in Linux have been a source of debate, contention and failure on the part of wireless equipment makers. They just can't seem to embrace the idea of Linux support. So, if you are buying a laptop and perchance might have a Linux future, you might want to research Linux wireless support for said laptop. What have other Linux laptop users been successful with?
As for my last piece of advice, "it's the network". I know the economy is sluggish or tight, depending on your perspective, and the cost of aquiring assistance with your PC hardware and software is going up too. Or maybe you just can't find knowledgable "and" helpful folk in the same person. If you own one these new fangle things called a computer, it might be a good idea to consider joining a computer club or user group. I am considering this as I don't know it all and I could use the networking, suggestions, help, resources, etc, etc, etc. The cost of membership is not that stiff and the committment in time is flexible. This kind of networking is good for all sorts of info that's on your level of experience. Older folk seem to do this more than younger folk. In the group where we have the Linux classes, there was a lady who used machine code and paper tape and did business programming, a guy who just bought his first computer and in between guys like me. It all makes for interesting conversations and laughs and support. The connections can help your career and on your resume you are involved in the community and continuing education for yourself. Linuxville has curbside cafes, you can kick back with a cool drink, light snack, wave at passerbys, chit-chat, dream, and explore ideas........