I'm not sure what particular part of approcket you want to duplicate, but it's main selling point seems to be the "find as you type" behaviour. A similar behaviour is exhibited by using the konqueror file manager. This can be extended with ioslaves.
Simply focus the address bar whilst in file manager mode, and an autocomplete box does the rest (for browsing directories anyway).
Using kioslaves allows you to browse systems other than your local file system. For example typing "settings:/" into the konqueror address bar will start you browsing system settings in the same way approcket does the windows control center. Google for "kioslave" to find out about all sorts of other stuff you can do with kioslaves.
Also checkout kiolocate for more powerful file searching in the same manner:
http://kde-apps.org/content/show.php?content=17201
Hope that's what you were after.
L