I usually open all sorts of files from within Ztree by hitting the letter “O”. Files like html files and gifs etc.
But, I couldn’t open .bmp files.
This has been bugging everyone for years (at least since 2004).
Here is a long-lost [ pixellated ] reply from the past:
Find the BMP.BAT file in the ZTW directory (usually c:\ztw for XP or c:\users\loginname\ztw for Windows 7) and rename it to bmpx.bat (or anything).
Now the .bmp files will open properly.
I think Ztree was trying to open PaintBrush (huh ?).