1) Laser guided missiles are a thorny and regular topic and not one of my specialities. Search the FAQ and the forum - its come up before.
2) Ed Depot - Tutorials - OFP File Formats - "How to put JPGs in your Briefings and Overviews" by Fishion.
You may need a special programme to take the screenshot: I use Hypersnap DX4, only because you can download it free from the net. Microsoft photo editor or a whole bunch of other things can be used to edit the picture once you have it.
You can get a .jpg -> .paa converter from the official websites. However, there is no point because the .paa is a larger file with no increase in quality (that I can see) and the .paa format can't be read by lots of programmes. Stick with jpegs.
If you can't be bothered to make a border, copy the one in Tutorials - Getting Started - "Tutorial Mission"
Edit the picture to the size (in pixels) that you want. When you save it however, there are rules on what dimensions it can be - Fishion will explain. In the Overview file though, you can make it any size you want again. In other words the save file can be distorted, in order to make the picture look perfect in the actual Overview.
For example: (the numbers here are just made up)
Create pic 97x41
Distort it so you can save it as 64x32
The html code in Overview.htm says its 97x41 so as if by magic its ok again.
Hope that makes sense.