terece, based on what you've described, I would stick with pre-built Windows computers, and I'll bet you could do it all with a budget of $1000.
I used to have Macs as well. (In fact, I had one with Final Cut-- Mac's professional level video editing software-- and a first generation DVD burner back when they still costed more than $1000 for a drive.) I will agree that, if video editing is a large part of your digital life, you're going to love the Mac's iMovie and iDVD for content creation.
That said, the Windows side isn't... half bad if you're careful. For example, I would completely skip over Windows Movie Maker, and go ahead and pony up for Adobe's Premiere Elements. If you get really serious, you can upgrade to the pro version. Premiere will also work seamlessly with Adobe After Effects, which anybody who has done video editing and special effects seriously will know what an amazing gem that is.
Plus, staying on the Windows side will be a lot more um user-friendly in terms of software selections later, and it will also help lower your costs. I like... nay, love Macs too, but overall, I agree that both the hardware and the software tend to be over-priced.
As for centralizing your media content (music, movies, etc), I would look into network storage. Don't worry, they're not as bad as it sounds. Basically, it's nothing more than an external hard drive with a built-in network card that you can stick into your home network. That way, the contents there can be shared with all of your computers. I'll bet if you shop around long enough, you could even find one as cheap as $100, but
I'd considering spending a little bit more for a terabyte drive, as they seem to be the sweet spot right now. (If it's a NAS and you have a static IP, you could even make that content accessible anywhere in the world, with internet access.)