Hey all, figured I'd give teaching a go. Faking Galaga text is surprisingly easy to do. This is a way I figured out how to do it.
Must note, this is just a way I came up with to accomplish the same effect. Just because this is A way to do it, doesnt mean its the ONLY way to do it.
For this tutorial, I am using Adobe Photoshop CS5 but it'll work with any photo-editing software that has both layers and stroke. This tut covers the font effect, not the font itself.
I also assume you have a rudimentary knowledge of photoshop.
First lets remember what the Galaga marquee looks like:

Next, lets remove the Galaga text from the background (this is where I assume you can already do this)

Also, now is a good time to copy that yellow "spark" and paste it on top of itself in a new layer. This will allow you to put the text under the spark where ever you want without having to worry about trimming around it later.
Next we add the text. Text color doesnt really matter, you can make it one of the final colors to make 1 step easier, but I just left it black.

notice that you can see a photoshop dialog box to the bottom right. This isnt part of the image but Im not a professional so Im not going to bother photoshopping out stuff like that

Here is where things get a little more...tricky.
You will need to right click the text layer (in my example it is called BYOAC) and rasterize the layer. Only do this step AFTER you are happy with the front size, shape, etc because any transformation of the font after this will add artifacts and other irregularities to the text.

Ok, so the color bands around the Galaga font in the factory marquee are black , orange, and red. In that order starting from the inside out.
You will now want to right click the text layer and "duplicate layer" each time you dupicate it, rename it "text - Black" ,"text - Orange" , and "text - red"
You should have a total of 6 layers. The background, Text , text- black , text-orange , text-red, top spark (if you duplicated the spark)

Its important that the layers be in this order!
Black is on top because the black stroke has to be on top of the orange, which has to be on top of the red. It'll make more sense at the end, I promise
The names are just so you know which stroke color goes on which layer. the default text can go anywhere under the top layer, its just there in cause you mess up a layer, you can just recopy the original. If youre ballsy or confident, you can safely delete this layer.
Next step is to make the font have a light green top and a dark green bottom.
text-black is the text layer on top, so thats the layer we will be coloring. Coloring any other layer wont matter because the text-black would be on top of it covering the colored font with the black. On the text-black layer, just use the paint bucket to fill it in with the top green color. If the paint bucket wont fill in the text, you have to right click it and rasterize the layer.

I know it looks silly, and you might have some weirdness along the edges, thats fine.
Next step is to slice a line out of the middle. So grab your rectangular marquee tool (the dotted box icon) and put a box around the area you want to be black in the middle, then select the magic lasso icon, hold alt and click in the white area. This will select a straight line along just where the font is.

Just grab the pencil tool and color in the selection black
Then use the paint bucket to fill in the bottom of the font with the darker green color:

Its starting to come together, right?
Next step is to double click the layer to bring up the layer style dialog box. Select stroke (at the bottom) and make the stroke roughly the same size as the black line in the middle of the text.

We are just going to repeat the "double click layer style dialog" for the remaining layers, making the stroke look the same size on each layer. starting with orange:

and finally red:

Your layer box should look something like this:

That pretty much does it, once you have the strokes uniform and you are happy with them, you can then merge all the text layers into 1 and put it where you want on the marquee.

An alternate slightly more advanced way would be to add the black stroke to the text after making it 2 greens with the black in the middle, then rasterize the effect, then stroke that with orange, rasterize the effect layer again, and finally stroke it with red. Totally fine way to do it, but I think keeping the strokes on separate layers makes editing them much easier.
Feedback is appreciated, and if you use this tutorial to make anything, I'd love to see it!