Hi Sid
Can you be more specific about the file you downloaded? I mean, what is it: a program, a picture, some kind of document etc.
When you get the "open with" box coming up, and are unsure of the program to use, make sure the little box for "make this the default program to open files of this type" (or whatever it says) is unchecked. that way windows will not use the same program if it's the wrong one.
Not knowing what the file's for, or where it came from, there's not much springs to mind for a *.ps file. The only thing I can think of if a photoshop macro or add-on, but that's a shot in the dark.
Sq