Yo Les! To summarize the above, There are "real" tube preamps that use big mucking power tubes, and "tewb" pres, which send part or all of the signal through a little tube in the front end of the amp, usually with an adjustable amount of tube effect. Tubes are used in preamps and mics to introduce distortion. In a guitar amp, that effect is obvious. In a mic pre or mic, the effect is intended to be more subtle. It decreases the accuracy of the signal, like airbrushing a Playboy centerfold so we don't see her stretch marks. There's lots of things in sound that you really don't want to hear. This effect is called "warmth" when we like it, and "muddy" when we don't. Once upon a time, *all* preamps and *all* condenser mics had tubes in them, and the world got along just fine.
In general, if you are buying a cheap preamp, a solid state pre is a better choice, and very few serious audio enginerers have much use for a "tewb" amp of any description. At best, it's an effect you use occasionally for something unusual, usually meaning that you can't get enough gain without dialing up some distortion. At worst, the signal is always running through that tewb, and you always have useless, nasty, distortion (and noise).
Real tube amps are often wonderful things, and they don't come cheap. The Groove Tubes "The Brick" is one of the cheapest real tube amps, at about $500. Really good ones are more likely $1000-$2500 per channel, and are to die for. If you aren't ready to spend at least $500 per channel on a preamp, I recommend solid state. I agree with a lot of people that the DMP3 is one of the cheapest preamps that doesn't basically suck. I'm saving my dinero now for a real tube pre, most likely a Pendulum MDP-1, which I love. Best of luck.-Richie