Ok, before I start, I just want to tell you that it took me
A LOT of practice to get this right.
So you might have to practice a few times before
You get it right.

But most of you are probably faster learners than me and I didn't have a guide so it should be easier for you xD
1. Ok, first, open up MS Paint (duh xD)
2. To choose a color for the background, click on your background color in the color bar under the picture, click on the bucket (circled in dark purple in the RTP above) and click anywhere on the picture.
3. Click on the Text button (it looks like an "A" with a box around it and in the RTP above it is circled in black.)
4. Make your text box by clicking and holding down the left mouse button on and dragging it to the demension that you want it at. (It is best to start at the upper left corner and go down about five inches maybe, if you want as little background as possible.)
5. Left click in the text box and select "Text Toolbar at the bottom of the menu that comes up.
6. Choose your font, size, style, and if you want it to be Bold, Italic, and/or underlined. (Make sure your color is black in the color bar under the picture)
7. Now type your text in the text bar.
8. Now, choose any color besides black.
9. Make another text bar over the letter
right on top of the black letters. This part is very important. If it's not on top of the text you're making, the shadow won't work.
10. Now type your text.
11. Now, on the bottom right corner of your picture, there should be a tinyyy little square in blue. Click on that and drag it upwards until only your text and a little bit of background show.
12. Wahla! The end result should look something like this (click the image to view it in full):
BI drop shadow siggie.PNG
(Optional) If you want a drop shadow siggie with circles, then before you start your text box, then click on the circle thing in the tool bar (circled in yellow in the RTP above) and make a circle, using black. Now drag them to make a circle. (Make sure that in the options with the rectangles at the bottom of the tool bar, you choose the first one if you want multiple colors. If not, then choose the last option.) (Remember to make as many circles as you need letters in your siggie.)
Now that have your circles, if you chose to make multiple colors for the circles then choose one color and click on the bucket and then click on the circle you want to be the color you selected. Then choose another color and do the same thing with the next circle, and so on. If you cose to only make it one color, then you don't have anything to worry about.
Now follow the rest of the steps, and you should have a circley-drop-shadow-siggie! xD It should look like this (I was making this in a rush, so normally I could make it neater):
BI Circle Drop-Shadow Siggie 2.PNG