Well, if you had Illustrator, all you'd have to do is choose a dotted line brush... not sure if there's a way to do it in Photoshop or not.

Create a pattern?

Just make about two dots that are equal in length and width. Then go up to Edit and go to Define Pattern... Then when you want to use the pattern just use the paint bucket tool and select under FILL: PATTERN. Should do it?

what about photoshop cs?

My method SHOULD work.

I'm really bad at explaining things online...

Can't you specify gaps in a brush line?
(I know bunk about Photoship, sorry.)

where do i got o select under fill: pattern?

You do not need a tutorial to walk you through Spacing, but you can take a moment and experiment on your own. Choose a small hard round tip, and increase the Spacing for it on the menu (see Figure 3.28 for an example). You'll see the continuous stroke break up into individual dots, and if you paint with the setting you've chosen, you can make a path of dots. Spacing is much more useful when the individual paint daubs represent something such as stars or other mini-designs on the Brushes palette. Painting with dots wears thin in the amusement department fairly quickly but could come in handy if you need to make a dotted line with evenly spaced dots.
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How to draw a simple dotted or dashed line (applies to Photoshop Elements also).

Have you ever wanted to just draw a simple dashed or dotted line in Photoshop? This should be simple, right? Well, it's not too complicated if you know where to look. But I'll admit, it is a little round-about.

Steps:
1) Select either the Pencil or Brush tool
2) Select the brush size you want to use for your dotted line (Hard-edged brushes work best). If you want a dotted line, use a round brush, if you want a dashed line, you will need to load the Square Brushes library. To do this, click on the brush size icon in the options bar, then click on the fly-out menu (circle with an arrow icon) and select Square Brushes.
3) Access the Brushes palette (it lives in the palette well by default), click on the 'Brush Tip Shape' to display those settings and change the Spacing setting to a high value (200 or more).
4) Draw on your canvas while holding down the Shift key, which allows you to draw straight lines.
(Tip: Click once to set down the start point of your line, move your mouse to where you want the end point to be, hold down the Shift key and click again. This works with any tool that uses brushes: Healing, Clone, Burn, etc.). If you want longer dashed lines, you'll need to create your own custom brush.

yeah, what he said :)