Transparent Background

In Photoshop...

1. FILE (ALT+F)

2. Save for web...(ALT+SHIFT+CTRL+S)

3. transparent

4. Matte: use whatever color is the background of the page.
( I used #FFFFF for the sample image, since that's the background color here )

5. click -> SAVE

Here's a sample image w'out the background...



This only works for .gif images