What's the smallest tank that can be successfully cycled?

So, while I'm waiting for my 55 gallon tank to cycle, I'm already thinking about my next tank.

The 55 gallon is my first big tank; my very first tank was a tiny 2 gallon tank which I kept on my dining table with a betta in it. Although Spot developed fin rot about 2 weeks after I brought him home (Petsmart or Petco, don't remember which), he lived about 3 years. Despite a multitude of antibiotics and other remedies, his fins never grew back to their former glory. There were no decorations in the tank other than a fake silk plant. I changed the water every week and conditioned the water with Prime.

I'm thinking about getting another similar tank and another betta. But I would rather not have to do a 100% water change on a betta tank every week. I'm also thinking about moving the cardinal tetras from the 55 gallon, since they don't seem to be compatible with any of the larger fish I'd like to put in there.

So, my question is (actually, I have two): what is the smallest tank that can reasonably be cycled? I've heard smaller tanks are harder to cycle and keep cycled. I know a 10 gallon can be cycled but that's too big for the dining table. Can a 2 gallon be cycled? What about a 5 gallon?

And secondly, could 7 cardinal tetras live happily with a betta? (Or, at least more happily than they would be living with 'peaceful' cichlids or rainbow fish?) Or am I looking at a third tank in my future?:help:

Thanks, ct. My 2 (or was it 2 1/2?) gallon came with an UGF but I never used it. It did have a 25W heater in it. The 100% water changes got kinda old after, oh, a year or so for both me and Spot; partial water changes sound much more doable. My dining table backs up against a stone wall and there is an outlet there. I'd like to have some gravel and maybe even a single low-light live plant in there. Sounds like a 5 gallon with filter and heater may be the way to go. And thanks for the info on the tetras. I'm not sure what we're going to do with them.