One way is to set a timer interrupt to increase a variable.
Then when the button is pressed the timer interrupt is enabled after clearing the variable. the longer the button is held down the higher the count,and use that value to increase a menu count etc.
ie

ET0 = 0;
Count=0
menu=1;
Do{
if((Count>100)&&(Count<200)){menu=2}
if((Count>200)&&(Count<300)){menu=3}

}while(!button)

ET0 = 1;
and so on..