there are lots of reasons you might want to change the default Solaris 10 login screen. here's the quick and easy instructions for doing it.

the file which contains everything you want to know is called 'styleModern'. making changes to this will create the effect you want without mangling too much of the standard config.

first, create direct /etc/dt/config/C, and copy in styleModern:
# mkdir /etc/dt/config/C
# cp /usr/dt/config/C/styleModern /etc/dt/config/C/styleModern

next, create a local images directory to hold your modified images, and copy across some of the basic items (which you won't customize)
# mkdir /etc/dt/config/images
# cp /usr/dt/config/images/A* /usr/dt/config/images/S* /etc/dt/config/images


now create your custom dtlogin backdrops as gzipped xpm files. you need one file for each of the likely screen sizes, and each file must be named in the format name-size.pm.gz. for example, mybackdrop-1400.pm.gz for 1400x1050 (laptop) screen, or mybackdrop-800.pm.gz for an 800x600 screen. save these files in /etc/dt/config/images .

# ls /etc/dt/config/images
Adobe.im1.Z mybackdrop-800.pm.gz Solaris.im8g.Z
Adobe.im8 Solaris.im1.Z
mybackdrop-1400.pm.gz Solaris.im8

now edit your /etc/dt/config/C/styleModern file, and make a couple of changes. change the line defining PIXMAPDIR from
#define PIXMAPDIR /usr/dt/config/images
to
#define PIXMAPDIR /etc/dt/config/images


and change the line defining STYLE_PIXMAP from
#define STYLE_PIXMAP PIXMAPDIR/styleModern-backdrop
to
#define STYLE_PIXMAP PIXMAPDIR/mybackdrop

(or whatever you set 'name' to in your files above.

save, logout, and enjoy the new backdrop!

to revert to the default, simply delete the /etc/dt/config/C/styleModern file