It would be better if the file type would state the search mask Code Files (*.bmx)!
It'll do that (in Windows) if the code specifies it explicitly. Note that you only specify the "*." part for the first extension in each group (otherwise the "*." shows up twice):
filter$="Image Files (*.png, jpg, bmp):png,jpg,bmp; Text Files (*.txt):txt; All Files (*.*):*"
filename$=RequestFile( "Select graphic file to open",filter$ )
Print filename
In my experience, this isn't needed in Linux (at least not Ubuntu, which adds the "*.whatevers" automatically). It doesn't seem to be possible in OS X at all (since it doesn't have a filter drop-down). Samples of Ubuntu and OS X requesters
are here. But in Windows, specifying it as in the code above results in:

Is there any way to get an output like this:
I don't know of a way to specify "details" view by default in code, but the user can select it via the icon at the top (and then further customize it as desired):

(Or were you talking about the "Windows 3.0 file manager" look with separate Name and Extension columns? I don't know of any way to do that with Blitz - or in XP at all, since winfile.exe isn't included.)