We need to know if you have xvesa or xorg.
What version of slitaz(stable-2.0 or cooking+release date),running off burned cd, usbkey, hard drive ?
Did you install xorg on stable or cooking prior to 2010 ?

all the versions I've tried seem to behave the same (2.0 stable and the last three versions of cooking) I'm booting from a USB thumb drive created with unetbootin. hardware is an HP t5700 thin client which has an onboard ati rage xc. behavior doesn't seem to change when I use slitaz screen=xorg. on bootup I am not presented with the resolution selection screen I get on other platforms I've tried. I tried transplanting the xorg.conf from puppy linux (which seems to work fine stock) but haven't been able to make it work. I'm new to slitaz and admittedly pretty half-assed at linux in general. any suggestions would be most welcome!

use slitaz-2.0 has xvesa
xvesa runs @ 60HZ the vesa standard which is what you request
in xterminal type

xvesa -listmodes

show all supported modes

xvesa -help

show all options
on a persistant or full install slim login manager starts xvesa with settings in
/etc/slim.conf
My /etc/slim.conf for ati rage2c driving 21" lcd 1440x900 display:
default_xserver /usr/bin/Xvesa
xserver_arguments -ac -shadow dpms +extension Composite -screen 1024x768x24

To bypass slim.conf and choose same resolution but fewer colors I enter this bootcode

slitaz screen=1024x768x16

When I try 1280x1024x16 my 1440x990 lcd gives me a black screen because 1024 is larger than 990.

The resolution setting of the video card must be equal to or less than the monitors rated max resolution.