One of the things you want to look into is pen testing:

http://www.google.com/search?sourcei...:en&q=pen+test

I gave you Google link as opposed to individual link so that you can see the vast array of information out there on it. That first site, Security Focus, is a good place to start.

If your ISP is running a MS Solutions environment then check this place out thoroughly:

http://www.microsoft.com/technet/security/default.mspx