The Vectrex overlays in this archive where converted by L Cordier.

I have made Spikesh.png and Moon.png with Paint Shop Pro 7.
See the wizard in export fonction PNG to proceed.
PNG work only if the file .PCX have a black background and only one transparency color!
The png made with Photoshop 6 don't seem to work with MESS.

So, I have used Xv and Netpbm from an unix clone:
OpenLinux Caldera Workstation 3.1 (I found it with a PC magazine).
Other linux distribution may also work (Suse, RedHat...).
Caution: You need to create an ext2 partition more than 1 Go.

I have followed the procedure describe by Mathis Rosenhauer.

Boot Linux with Lilo, start KDE (window manager), and execute XV.
Load a PCX picture from directory DVE/PIC. The picture must be : 1600x1200x256.
For example load MrB-CS4.pcx, clic/autocrop, clic/save
Format: pbm/pgm/ppm(raw), colors: full color, check normal size, type MrBoston.ppm, clic/save

Info: if you load MrBoston.ppm in Xv, you need to set picture to 8 bit-mode.

Clic Windows/color editor, clic/grey, clic on RGB/HSV
For each color adjust the third cursor "Value":
0 = full transparency (useful for AGT, Vaders where background is black with a lot of colors to display)
20= transparency of the overlays (in Webwars Green and blue background value = 20)
255=opaque like the logo,text and border.
clic/close, clic/save, Format: pbm/pgm/ppm(raw), colors: greyscale, type MrBoston.pgm, clic/save

Now start a xterm session and type:

cd /blabla (where blabla is the directory with MrBoston.ppm and MrBoston.pgm)
pnmtopng -alpha MrBoston.pgm MrBoston.ppm > MrBoston.png

Move MrBoston.png in MESS directory /artwork, reboot, start Windows and finally enjoy !
(perhaps ;-)