1. OPEN the background tile image you're using on your web page. Make sure you change the mode to RGB color (IMAGE/MODE/RGB COLOR) if you background is in index color mode.

3. Now what we wanna do is find the "average" color of your background tile image. To do this, we apply a gaussian blur (FILTER/BLUR/GAUSSIAN BLUR) of about 32 pixels. It doesn't have to be 32 pixels, you just want it to wash out all the detail until there's only a few colors left. These colors are the average colors of your background tile.

4. We're gonna use one of the average colors to fill our new document, so pick up one of the colors with the eyedropper tool...it doesn't matter which one you choose since they're all very similar colors, so just pick one at random.

5. The background tile image was only used to get an average color, so if you want, go ahead and close (or minimize) the document...it won't be needed for the next step.

6. Now we start getting to work, Create a NEW document with enough room
for whatever it is you plan to make.

   IMPORTANT:
   Make sure the contents is NOT transparent, use WHITE or BACKGROUND
   COLOR.  If you don't, which is a very common mistake, your
   background that you think is transparent will actually turn white,
   and you'll have ugly white border around your text.  Why is this?
   Well, the transparency in Photoshop has *nothing* to do with
   transparency used in GIF89a files.  The mode should be RGB also
   (unless you know what you're doing).

7. Hopefully the average color from your background tile image is still the current foreground color. If it is, use the paint bucket tool to fill the entire document with the foreground color. This is the color we'll be working on now.

8. Once that's done, you can create whatever it is you wanna created for your web page, in this case I drew a simple logo that says "GIF89a".

9. Now that you're finished, you have to reduce the colors down to 256. To do this, click on the "IMAGE" menu, down to "MODE" and over to "INDEXED COLOR". GIF89a only works on index'd color pics. The settings are up to you, but I usually use "Adaptive" and "Diffusion". Oh, and if it asks you to flatten the image, click OK...gif's can't use layers.

10. Now's it's time to convert it to a GIF89a. Click on the "FILE" menu, go down to "EXPORT", and over to "GIF89a Export". You show now see something that looks like the image below...if not, most likely you're not in INDEX'd mode.

11. Basically all the gif89a exporter wants to know now is which colors you want to be transparent. So all you have to do is use the eyedropper tool to select a color (or colors) that should be transparent. It should look like this once you've selected your colors:

After you're done, click the OK button and it'll ask you to save the file, type in a filename, click OK and you're done! Simple, huh?