If the main purpose of using a .gif file is for the web, then there most certainly is a way to make your image (or parts of it) have transparent qualities.

It's actually quite simple.

On a layer, make a grid of pixels of alternate colours, one the colour of your background and the other transparent (or simply omit to apply a colour). The result should be a very fine chequerboard effect. Move this selection over your image and you'll see that only the pixels that are transparent will allow the underlying image to show through. Save the file as a .gif and make sure that the solid/background colour in your image is rendered as transparent.

Now when you use this in a web page, you'll see that whatever is underneath it will show through. The size of the grid can be altered to give various degrees of opacity. This is not a perfect method but it works pretty well. Forget alpha transparency in web pages, they're really not ready for the .png file format yet.

Hope this helps...

Greg.