How to setup resolution for XBMC

Hi guys,

I need a little bit help for setup resolution on Angstrom for XBMC.
When I start XBMC, only a black screen appears.
I read a little in this group and now I know I should change the
resolution to omapfb.mode=dvi:1280x720MR-24@50 or something else,
but I don't know how to do.
Can anyone help me with a step by step tutorial for Beagleboard noobs.

I try this in HyperTerminal,

setenv dvimode 1024x768MR-24@60

and it works!!!

But there are 2 problems:
1. when I start XBMC the screen is still black, no GUI
2. when I restart Angstrom the screen have the old resolution 640x480

How can I fix it?