Testing the strength of windows on my network. How?

Hi. I have created a local network that consists of the following:

1. Modem-router
2. Ubuntu (desktop machine)
3. Windows (laptop machine)

*all connections through ethernet

I am using my laptop in various places and have always been concerned about
security risks. Therefore I would like to teach myself how to:
1) Discover how "strong" really windows is
2) Discover possible security risks and how to tackle them
3) Gain overall knowledge on network security issues

I have heard of some educational tools that provide already vulnerable environments to teach you some of these but that's all I have heard off.
Could you suggest - pdf- e-books - tools - white papers - to read/use in order to achieve my goal?

Thanks in advance.

P.S. I will experiment only on my own network and machines. I really just want to know how "hackers work" to prevent them from hacking in. No planned attacks for banks, NSA, NASA, wargames or whatever. Just seeking knowledge that is already out there for basic stuff ;).

One thing to check out is zenmap, the GUI frontend for nmap. It will do port scanning and give you advice. It should be available in the repos. A good tool for beginners and experts alike.

For more information and news on security and stuff, here's a couple good places to look.

http://www.grc.com/default.htm
http://www.grc.com/securitynow.htm --regular podcast, but be sure to listen through the archives as well.
http://www.gnucitizen.org/
http://insecure.org/ - a little creepy, but informative. :-P

Thanks, mate.
I really appreciate it.