Is an RIS rail compatible with Weaver/Pickatinny?

[B.D.Dubloon]

I am looking at getting a cheap fore grip/bipod for my G22 and I was wondering if something made to fit an RIS rail would work on a weaver or pickatinny rail? As a side note, what is the difference between weaver and pickatinny? Are accessories for one good on the other?

Thanks for the help,
BDD