It's right from your Bitmit ad! You listed the 420 XRP with a "Buy it now" price of 0.07 BTC. That comes out to 6,000 XRP per 1 BTC = (1 / 0.07) * 420 unless my math is wrong?
Go to Advanced, Trade, and then for Base currency press Change issuer and enter Bitstamp's address (rvYAfWj5gh67oV6fW32ZzP3Aw4Eubs59B I believe). You should probably add Bitstamp as one of your contacts in the wallet then you can just use the name instead of repeating the public key.
After you have set up the issuer choose BTC/XRP as your currency pair then press "Order Book" and you will see the bids and asks.
Ah, yes, I had not added them to my trust, FYI the address was different for me, As I would think it should be for everyone? But I get it now Thanks!
Do you know if its true that people need a few hundred XRP's to get started on BitStamp and other sites? I got mine by posting in the giveaway thread. What would a fair price be for 420?