Once again guys...from a true 'puter geek standpoint:
If you don't know the sender, DO NOT OPEN THE ATTACHMENT..PERIOD!
If you do know the sender, still be leery but consider their past history. Most people don't send files that are ".exe" or ".vbs" etc.. If someone typically sends you things in a zipped file, like pics or .txt documents, feel free to open them.
NOW...this is important. Many viruses/worm programmers know this and name their files something like this "sexy.jpg.exe".
Now, assuming you know that a buddy has sent you picture files in the .jpg format, you open it. The above is not a picture but an executable file (.exe is the last part of the file name) which could be a virus. Look for extra extensions in the name of the file.
I've really only scratched the surface of tips on this topic but I hope this helps.
Here's a Free and fully functional anti-virus program that I have used successfully for years...go get it if you don't already have one:
http://www.grisoft.com/us/us_dwnl7.php?ver=31
Have a great day and don't worry, just be cautious. And remember, back up files on CD (doesn't cost that much anyways) that you would need to keep. Imagine that your computer was useless tomorrow...what is irreplaceable on it?
If it's irreplaceable, back that stuff up now!
I hope this was helpful to at least someone here. Remember, don't worry just be cautious and prepared.
-Mark Holman