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thanks for repyling Chris, you are right about these .zip files and folders being associtated with Explorer. The problem was I could'nt change it back as there wasnt an option to do this in the list that came up. I even unistalled the program it had mistakenly become associated with and it reverted back to default, but as soon as I re-installed the program, the association came back. I finally had to use system restore (a bit drastic I know) but it worked and things are now back to normal.
Z.