I've taught Microsoft certification classes from Microsoft "Official" curriculum, and I've seen a lot of third-party books. Too often their exercises are grounded in walking you through installing or configuring a feature, and they never give you any real-world grounding in why you might use a given feature. I've met a lot of people who, as a result, walk around looking for applications for esoteric features but don't know why they'd use the features.
Identify real-world scenarios that you'd like to mock-up. If you want to learn about Group Policy for example, setup a goal scenario based on ways that you see Group Policy used at work (or, if your workplace is one of the countless shops that doesn't use Group Policy, a way that you'd like to see Group Policy used) and have at it.
Virtual machines are great, but be careful not to get mired down in dealing with the virtual and forgetting about "the real". When it comes to more esoteric things like configuring Ethernet VLANs, WAN routers, firewall devices, etc, there's a lot to be gained with the hands-on plugging-in and unplugging cables. There's something to be said for having at least one physically dedicated client computer for testing, too. You can get a real feel for how much it "costs" (in time) to move data across network pipes in a way that virtual switches don't show you.
A home network is great, and I think you should definitely do it. Beware, though, that a home network teaches you very little about how business uses computer networks. Frankly, Windows server admins are a dime a dozen. A sysadmin who has an understanding of the ROI model of technology in a business is a different animal entirely. You certainly should learn about technology, but you should also learn about business and the management / application of technology in a business.
I'm at a loss as to where to point you in the way of books / training materials because I've been almost universally disappointed with such items. I'd encourage you to see out mentors. You might find that in your workplace, at a local user's group meeting, or on the 'net. If you have the capability to pull a few extra unpaid hours working with the network administration staff at your job, give it a go. If not, perhaps you can find an internship gig on the side by way of local volunteer organizations or by enrolling in a community college. There are a lot of possibilities if you're willing to go out and look for them.
re: Windows Server 2003 versus Windows Server 2008 - It pays to be conversant with both. They're not that different (W2K8 feels like a slick service pack to W2K3, to me) and you shouldn't be intimidated to move freely between them. Learn where the differences are by way of "what's new" guides and docs, and learn what those differences mean with respect to real-world applications.