You're welcome for the info. Remember Adobe is the legitmate .pdf reader, get used to seeing what it looks like. You will usually see their icon that looks like this:
http://get.adobe.com/reader/?promoid=BUIGO On sites where you need to view something they usually have a little rectangular icon and a message that Adobe reader is required to view the file. It is free, and it does often prompt you to upgrade after you've installed it. When you do -- again you have to be careful -- because even Adobe might try to get you to install a tool bar on your menu. So uncheck boxes that want you to install unecessary items during the download.
It's the other big flashy ones (like that green one) that lead you to believe you have to install them to view whatever you are trying to see that will mess up your PC. Most XP and Vista PCs create restore points when you download a new program, and you can usually access "system restore" under "accessories" and "system tools" on your start menu if you need to revert to the state your computer was in before you downloaded malware or other programs you do not need.
Trojans require more effort to get rid of, and you need to have good anti-virus and malware protection installed. and update it frequently. If they do not work you can go to
http://housecall.trendmicro.com/ and use their free "housecall" scanner. If you do, be aware that it takes forever to download and scan the first time, and it IS working.