Help setting resolution to 640x480

[porga]

So I have eee PC with openelec installed. Its native resolution is 800x480.

Openelec spits out 800x600 through VGA port automatically and shutting Laptop screen off, which is realy nice feature.

I hooked it to 55cm 4:3 CRT TV at this moment, the problem is that text is hardly readable on such resolution.

I would like to "force" 640x480 when External VGA convertot device (or monitor) is connected, can someone point me how to?

Or i would like to increase default font size in XBMC, maybe that would help?

[porga]

EDIT:
no need for lower resolution, I found theme with large Arial fonts, Transparency!