How Can I Set Which Categories Are On Top and Side Bars?

I am using the default theme with 1.5.4 . How do I determine which categories will be on the side link bar and which ones will be on the top link bar?

Thanks in advance!

if it's he same as 1.5.1
login to admin
select catalog > categories
select the category you want to position and click edit
click the data tab
scroll down to where the check box for 'top' is
select or not
save

Great, thank you!!