Right. Gonna teach you some easy stuff, that I actually found out by coinsidence.
'tis very easy. We're gonna do this:

Mkay? Great stuff.
So. Lets' get cracking.
If you just made it in Photoshop, click the
"Go to ImageReady"-button. The very lowest on your tool panel.
NOTE: You have to merge all layers (Layer -> Merge All...).
NOTE²: If it's a file you've imported from another image file (opened it directly in ImageReady), Select it all (CTRL+A) and
go File -> New... - The format should be ok. Click ok. Then press
CTRL+V. Your image should look excactly the same as before, but in no format.
Mkay. You should be in ImageReady now. Start by opening the Animation Window (
Windows -> Animation).
Let's say you start with this:

Shouldn't be a big deal.. Just - don't make the font white. Make it a gray nuance - remember the glide is to be white.
So. Start by zooming in (I did 800%) on the object you want to give the effect. Use the
Rectangular Marque Tool and select the text areas,
making it look somewhat like this:

Mkay. Now Copy the parts you've selected (
CTRL+C), and press delete. It should now be looking just the same. Visually. Press CTRL+SHIFT+N[/b]
to create a new layer. Now if you look down, in the right corner, there should be a "
Layers-tab". Sort the layers like this:

The front layer, is the layer that you started with and deleted the text.
Number two in the order is a totally new layer, that is empty (The one you just created)
..And the third is the text itself.
Now, for some explanation. The middle layer is the animation effect. You want it to be between the front layer and the text, because it's
supposed to be on top of the text, but below the front. Logical, right? Good. Now, let's proceed!
Good. Now select the middle layer, and the pencil tool with a white foreground. You can put the middle layer on top to help you - just put
it back down when you're done, mkay? Good. Draw something like this:

Right. Put it back down and it looks like this:

Mkay. Now drag it away from the picture, to this position:

You're gonna see a very faint outline of it. Nothing like this. It's gonna look like this when you let go:

Mkay? Good.
Now go
Window -> Animation. A bar will pop up, looking like this. Click the button the arrow indicates.

It's gonna look like this when you're done:

Mkay? You're gonna have a whole bunch of frames later. Good. Now
click the move tool and nudge the glide-layer
4px to the right. Just press
your right move key
4 times. Mkay.
Should now look similar to this:

Nudge 4 times again...

..And again...

Just keep going 'till you're out of the image.
Okay. You should now have a hell lot of animation layers (frames). Good.
Mine looked like this:

They all say "0 sec." at the bottom, followed by an arrow. Go to the last animation layer and click the arrow. Select either 5 seconds or 10 seconds.
You can define your own aswell, but I chose 5 seconds.
Now go
File -> Save Optimized As...Enter the Filename and Location.
Note: Save it with no spaces. It's gonna replace spaces with an Underscore (_) Anyways.