Well I would definitely get a train pass. Check out the Cheap Trains link on the left and you'll find a pass that's good for you. It's really convenient and with two people you can usually get a group rate.
Stay in hostels (also check out the links on the left) and pic yourself up a good LonelyPlanet
Europe on a Shoestring book too, I found it indespensible.
Self-cater instead of eating out, and that's about all you can do to cut costs

Maybe try and get a student card if you're eligible and you'll get discounts at many museums too.
Have fun!