The leaving your wireless network open question reminded me of this.
I typically share the root drive on my machines across my network, and tie login authorization to the machines NT ID, so there is at least some form of protection.
My question, how easy is it to gain access to these drives for ill good? Is the authorization enough, or should I lock things down more?
I can't answer the main question, but do keep in mind that Windows, by default, is always sharing the roots of your drives. Try:
\\yourmachine\c$
(And then try not to freak out.)
If this is a home network with no wifi or secured wifi, it's probably not an issue. Your isp will almost certainly prevent anyone from trying anything via the larger web.
If you have open wifi, then there's a little more cause for concern. If it's properly secured so that some authentication is required, you're probably okay. I mean, a determined hacker could probably break in, but you're not likely to find a determined hacker in wi-fi range. But the risk (if small) is there. You will want to make sure the administrative shares (the \\yourmachine\c$ or \\yourmachine\admin$ mentioned earlier) are disabled if you have open wifi. No sense making it too easy.
Windows generally protects shares via two methods - permissions on the share itself, and then NTFS file permissions. Good practice would be to have the share permissions as "Authenticated User" and remove the "Everyone" group.
Personally I would make sure that usernames and passwords match up on each computer, and control permissions like that, rather than using computer name.