First thing, SheenaRead, never open email attachments unless you know what they are. Always save them to your hard disk first and scan them with your antivirus software. If you don't have antivirus software installed, your first priority should be to install some. To that end, click here and download the free version of AVG, it will keep your computer free from viruses. Do that now. When AVG is installed and you have done a scan of your computer to make sure it's free from viruses, you're ready to go on in the knowledge that you're virus free.
AVG places an option on the right click context menu so that when you right click on a file you can scan that file with AVG to make sure it is safe to open. In your case, with your email, and all attachments for that matter, rather than choosing OPEN, choose Save to Disk and save it to your desktop or a specially created folder somewhere, as long as you remember where it is. When you have it saved to disk, go to where you saved it and right click on it and choose "Scan with AVG". If all is clear you can then open it.
This is where you have the problem, Windows doesn't know how to open it. To show Windows how to open it, you need to know what type of file it is. To find out the file type, look at the file extension, that is the three letters after the . in the file name, for example .jpg, .htm, .gif etc. If you can't see these file extensions, Open "My Computer" and go to Tools > Folder Options > View tab and untick the litle box which says "Hide extensions for known filetypes", click Apply, click OK and close "My Computer". You should now be able to see the file extensions of all files, it is that extension that will tell you how to open the file. Let us know that extension for further advice.