First off, make sure your using the hacked version of Z26 from my website. You can get it on the downloads/applications page at 
http://home.comcast.net/~cpviewer . It's much more cabinet friendly and allows you to remap the keys using an ini file. That being said, here are two interesting exerps (sp?) directly from the readme file, probably in your /docs folder:
Configuring z26
    z26 has many options that are set with command line switches. You can
    use a text editor like Notepad to create a file called z26.cli in the
    directory that contains your ROM images to set these options. Otherwise
    if you type z26 with some command line switches and don't include a
    filename, the command line switches are recorded in z26.cli
    automatically as emulator defaults. These defaults can still be
    overridden with command line switches that you include on command lines
    that include a filename.
Video Modes
    Note that by adding 10 to the video mode number z26 will run in a
    windowed mode. Otherwise z26 runs full-screen. On some systems, windowed
    modes are very slow. So for maximum performance you should run
    full-screen. Adding 20 to the video mode number causes the game to run
    full-screen with the number of bits per pixel as your current desktop.
    This allows the phosphorescent effect to work in full-screen video
    modes.
    Mode 0 -- 400x300 (default)
    Mode 1 -- 320x240
    Mode 2 -- 320x200
    Mode 3 -- 800x600 scanline/interlaced
    Mode 4 -- 640x480 scanline/interlaced
    Mode 5 -- 640x400 scanline/interlaced
    Mode 6 -- 800x600 double scanline
    Mode 7 -- 640x480 double scanline
    Mode 8 -- 640x400 double scanline
Pretty interesting, eh! Here is the contents of my z26.cli file:
-v21-r60
Good Luck,
John