Jquery :: Executing Block Of Code Every X Seconds?

I'm working on a simple slideshow made with jQuery. What I'm trying to do now, is to make it change image every X second. I know how to change image, but i'm kind of stuck trying to find out how to make it "do something" every Xth second.

Here's an example: (obviously not working..)
function slideSwitch() {
//change image...
}
setInterval(slideSwitch, 5000);
//make the function slideSwitch execute every 5th second.

Also, is there any "else if" function in jQuery? Like in for example PHP, you can use "if", "else if" and "else".. like this:
if(){
}else if(){
}else {
}

So is there any function like that? I googled it, and I found out I have to use some kind of plugin for it to work? How do I use it?