What exactly is this "double standard" treasure that many monsters yield? I haven't found any info on it in the books. And BTW what is a "standard" treasure?
As for your questions. Double Treasure is simply double the standard treasure amount for an encounter of that EL. Standard Treasure is done by EL and appears on p51 of the 3.5e DMG as a table in the middle of the page.
EDIT: If you are new to DMing or to 3e I would recommend you take a look at this. The Dungeonomicon Especially the 5th part about Economics in D&D. There are a lot of gems for a DM and player in there.