Unsigned certificates/unknown publishers?

I am having a problem downloading necessary software, Flash Player, driver updates, etc., and a dialog window opens saying that "Windows is protecting your computer by blocking this site due to unrecognized publisher" and/or certificates. I tried changing "Custom" settings in the Security section of IE6
Internet Options. Also tried unchecking Proxy server in LAN settings in the Connections section of same. There is probably a simple solution but I have
no idea where to find it. Requesting assistance from all you Major Geek experts and forum visitors.

Thank you -- rendover :confused

 

Not sure -- this is on a LAN at church and I've been asked to learn how to use a presentation utility for services and then incorporate it into Power Point. The software needs Flash Player 9.0 to display it's media and although Macromedia is a "trusted site" their computer keeps blocking the download and issuing a warning about unsigned certificates.:mad The IT person is not available to assist me so I thought I'd ask here. This computer also refused Microsoft's certificates as invalid. I'm stumped or I'm stupid, take your pick.

Thanks for your reply plodr. -- rendover