Okay. In order to extract the ROM files, you need to have a program that can handle .RARs. So go to http://www.jzip.com/
and download it with the button. (just an example, 7zip and winRAR work too but this one's free). Now you open the Pokemon_Light_Platinum_Full_English.rar file with jZip. You should see some files in it, including VBA and the .gba file. Then you extract the .gba and the .sav to a folder. You can then start up VBA, and open the .gba.
I THINK that's all you need to do to play light platinum, Miles said that the .ips adds a patch to the game, but I have no clue about that. Sorry if this didn't help a lot.