Oops! Sorry for the delay in responding, I was out riding!
I'm actually the happy owner of two touring bikes, both of which were custom-made for me. Corsair and Emily are right - I highly recommend a Bike Friday. I have an Air Glide set up for touring, and a Pocket Rocket set up as a road bike. And my other touring bike is a diamond-frame bike custom-built by Peter Mooney. I believe there are more touring bikes out there than there were when I bought my Peter Mooney bike, so it should be possible to find one - but to be honest if you're planning trips to Europe, it's much easier to fly with the Bike Fridays. As Emily said, they fold into their own suitcase, and then the suitcase converts to a trailer for cycling. And hey - you can even see a picture of me with my Air Glide on the Bike Friday web site in the What do you do on a Friday? page!
Bike Fridays are made to order, and the timeframe for delivery (obviously) is dependent on their current order level. There is another option there though, and that is to ask what used bikes they have available. As a bike manufacturer who likes to keep their customer base happy, Bike Friday will let owners who want a different BF (as opposed to an additional BF) use their current bike as a trade-in toward the purchase of a new bike. They do refurbish the bikes, so I would be very comfortable picking up a used bike from them.
Is there some reason you are leaning toward a mountain bike? You can get the gearing you want without going with a mountain bike by mixing components. Both of my touring bikes have a mixture of Ultegra (road) components (front derailleur & cranks) and XT or XTR (mountain) components (cogset and rear derailleur). I prefer drop bars, and I have Ultegra shifters. The reason I mixed the road and mountain components was to get the low gearing that I wanted - and that's quite a common thing to find on a touring bike. Unless you're planning off-road touring I would stay away from mountain bike tires - a smooth (but not skinny) tire works for touring. My favorites are Conti Top Touring tires - I've had many successful miles of touring on them.
If you want to do more reading, I have journals about all of my solo bike tours up on crazyguyonabike.com. You can get directly to the list of my journals at denisegoldberg.crazyguyonabike.com.
If you have more questions - please ask! And ask as many times as you need to! (One word of warning though, I will be somewhat out of touch from June 23rd through June 30th since I'm heading to Maine to go on a bike tour - you can follow along at Red-clad feet on a purple bike.
--- Denise