How to change AppleScript path to a Terminal-style path

I have a custom Service that I've created in Automater (I'm on OS X 10.6.5). The Service executes an AppleScript which in turn executes a shell script. Here is the AppleScript:

on run {input, parameters}
    -- do shell script "/usr/bin/find " & input & " -type f -name .DS_Store -delete -print"
    display alert "Path: " & input
end run

The problem is, the path passed by the Service (in the variable input) looks like:

Macintosh HD:Users:Matthew:Documents:Programming:Apple Scripts:

And for the command to execute properly, the path needs to look like:

Macintosh\ HD/Users/Matthew/Documents/Programming/Apple\ Scripts/

So, is there a way to translate the first path to the second path? I was hoping for a core function which handles this. But I suppose some kind of regex/find/replace/etc would work? I'm familiar with HTML/CSS/Javascript/PHP, not with Cocoa/AppleScript/C. Any direction or suggestions would be great!