Want to travel Europe on trains with only backpack and stay in B&B's. Thinking of starting in Romania and ending in London. Any ideas. Oh, and we really don't know much about trains, only what read on internet. Thinking of a 30 day trip.
Try Lonely Planet Europe on a Shoestring:
http://shop.lonelyplanet.com/europe/europe-on-a-shoestring-travel-guide-8/
The focus of your planning now should be choosing which cities you want to visit along the way and what sights most interest you there. You may be keeping some decisions flexible, but the more you know in advance, the faster you can make decisions on the road. See a variety of general trip planning topics at http://www.ricksteves.com/travel-tips/trip-planning.
Anything that you need to know about trains IS on the internet; start at http://www.ricksteves.com/travel-tips/transportation/trains. Train travel time from Bucuresti to London is only about 36 hours by the fastest route (via Budapest, Munich, and Paris), but you probably won't stick to that path. Train travel across the Continent (but not across the English Channel by Eurostar) can be covered by a Eurail Global pass (priced from $500-1000 depending on your age, number of travelers, and how many days of the month you want covered). Whether or not that's a reasonable value also depends on your specific route plan. If you're considering using a rail pass to get to Paris, then that leg of the trip should be reserved weeks in advance.
The best source of information about train travel in Europe is "The Man in Seat 61" website. Start by reading through that site.
If this is your first trip to Europe, I'd also suggest reading Europe Through The Back Door prior to your trip. Once you have an Itinerary worked out, use the country-specific guidebooks to plan sightseeing, transportation, lodgings, etc. in more detail.