I have been getting the following problem since I downloaded Acrobat Reader 7. Every time I try to open another type of file, for example a Word file that has come as an email attachment or a file from "my recent documents" my PC tries to open it using Acrobat Reader and I then get an error message telling me "Adobe reader could ot open "filename" because it is either not a supported file type or because the file has been damaged (for example, it was sent as an email attachment and wasn't correctly decoded)"
If I right click on the file and then click on "Open with>Microsoft Office Word" I can then open the file. But why is my system trying to open it with Acrobat Reader and how can I stop it from doing this?

I suspect that when you installed adobe reader you made it the default for opening all files.
If you go to start > control panel > folder options > file types and scroll down to microsoft word document for example. Highlight it and it should tell you what programme is used to open it. If it's the wrong one click change and choose the correct one from the list.