How do I make borders even?

I am using Photoshop 5.0 and when I use the rectangle marquee to create my border around a picture it seems like my border is never even on all four side. How do I make sure it is even?
Sorry for the basic question but I am still learning photoshop.

Thanks,
Senna

You hold in the shift key when making your selection. That gives you a square selection.

make a biger border than just a pixel