I'm assuming with no other example that your problem is that you want them to be horizontal instead of vertical (you say they are all on the left). If this is not the problem then this answer will not apply.
You probably want something in your css along the lines of:
li {display: inline-block;}
You may want to look up exactly what inline blocks do but in a nutshell it means the block is not the full width of the screen but just wide enough and the blocks act like inline elements meaning you don't start a new line with each one.
You will of course want further styling to make it look good but this should do the trick I think.
http://jsfiddle.net/NqgZ4/ for a jsfiddle example.
As a followup to your comment to have them spread out then the easiest way is to apply a width to them.
li
{
display: inline-block;
width: 19%;
}
Note that I use 19% instead of 20% to avoid rounding issues that may cause the width to exceed the pixels (eg if the width available is 999 px then 20% would make each of them 200 pixels which would then add up to too much).
If you have a dynamic number of menu items then its a bit trickier and I'd start thinking about a bit of script to equalise them (by setting the widths dynamically) though there may be a pure CSS method that will work with variable number of items.
Updated fiddle: http://jsfiddle.net/NqgZ4/1/