i have made something simple up for you (based on your description), just to point you in the right direction:
check it out here:
http://jsfiddle.net/ACenH/7/
function slider(container, delay){
if ($(container).length){ // checks if the slider exists in your dom
container = $(container) // select the container elements and set them as variable
var slides = container.length, // gives back the total LI's you ahve
slide = 0 // set the actual li to show
setInterval(function(){ // set a Interval for your main function
if (slide == slides) { // if the actual slide is equal the total slides the slide counter is set to 0
container.slideDown() // and all slides a shown again
slide = 0
}
container.eq(slide).slideUp() //slides the selected slide up i think you could think of a solution with .next() instead of eq()
slide++ // slide counter +1
}, delay)
}else{ // if the slider does not exists in your dom nothing happens
return false;
}
}
slider('ul > li', 2000) // call your slider function