To create a seamless graphic, you will create a box image that will tile horizontally and vertically.

Step One 

Open Photoshop and create a new image with the following dimensions:

Width: 300 pixels
Height: 300 pixels
Resolution: 72 pixels per inch
Color: RGB
Contents: White

Step Two

Pick a foreground and background color by double clicking on the foreground and background boxes.

Step Three 

To create a cloud effect, select the filter menu and the render and cloud options.

Step Four

To create a seamless pattern, select the filter menu and the other and offset options.  In the offset box,, select 150 pixels by 150 pixels and the wrap around option.

Step Five

To clean up the middle seams, use the rubber stamp tool.  Click on the rubber stamp tool and select an area that contains the pattern you would like to duplicate.  Simultaneously use the ALT key and a mouse click to pick up the pattern.  Then click to paint over the lines.  Instead of painting the whole area at once, it works best to paint a small area and repeat the ALT + Click process to pick up additional areas of the pattern.

or

Clean the seams by clicking on the blur tool and dragging over the seams.

Step Six

Save the image as a JPEG image using a small file size option.

You're Done!
The next step is to place this image on your web page using FrontPage.