Code:
///////////////////////////////
#include <acknex.h>
#include <default.c>

///////////////////////////////

FONT* fnt_test = "arial#20";
STRING* str_res[6];

PANEL* pnl_res = {
//	digits(10, 10, "%s", *, 1, str_res[0]); //wont' work, string is not yet initialised!
	flags = SHOW;
}

void main(){
	
	str_res[0]= str_create("600x480");
	str_res[1]= str_create("800x600");
	pan_setstring(pnl_res, 0, 10, 10, fnt_test, str_res[0]);
	pan_setstring(pnl_res, 0, 10, 30, fnt_test, str_res[1]);
}
though you'd be better off using TEXT instead of PANEL
Code:
TEXT* txt_res = {
	font = fnt_test;
	pos_x = 300;
	strings = 6;
	string("600x480", "800x600", "1024x768");
	flags = SHOW;
}