Today's podcast from TechNewsRadio.com covers an item from the July 2005 edition of PC Magazine. The article is entitled "Make Your Network Safer By Attacking It: A number of excellent tools can help you find out where you're vulnerable" by Larry Seltzer.
Professional tools mentioned include: AppDetective , Retina, and System Scanner; and check out "Network Security: Know Your Weakness" for details on these.
For self-assessment, examine: Microsoft Baseline Security Analyzer and NeWT Security Scanner from Tenable Network Security. There is also another open source tool called Nessus that I have had good experiences with in the past.
Bottom-line though is I highly recommend that you consider doing a vulnerability assessment on the systems you utilize and support both at work and at home.