Ave Cogito Ergo Sum,
I can answer your question about where to put the decks.
If you are running Windows, the decks should be unzipped to [drive designation]:\Users\username\AppData\Roaming\Forge\decks\constructed (or commander for commander decks.
I am not sure how to force the AI to play random decks but, in this section you will find a zip of decks designed specifically for the AI and many of these decks have specific difficulty settings.
Curiously, I have not experienced many problems with AI play. It seems to play most decks competently and sometimes brilliantly. I hasten to add however that I have downloaded over 12,000 decks so I may have been lucky.
I play four of the programs with AI offered on this site, namely, Forge, Manalink 3.0, Magarena, and BotArena. They compliment one another very nicely. Each has strengths and weaknesses which I expect from AI applications but that said, kudos to the developers of all of these games.
Anyhow, I hope you have fun with decks you have downloaded. While you're at it, try Forge's rather robust search engine in the deck editor.
As an aside, I will be adding a new topic and adding decks from a number of databases not represented here. User gos has done a superb job of scouring the big sites and has done considerable work in bringing these decks to the community. At the moment, I am looking at how best to add approximately 200,000 MORE decks from lesser known sites. It's proving to be a bit weird but I am hopeful that by next week, I SHOULD have at least 100 zipped and posted for community testing.
Salve,
Vlad
PS: If you cannot find the complete path, you will need to have Windows show hidden files and directories. If you are a Mac user, I am afraid I cannot help you but I am certain that someone else can.