Training & Nutrition - n00b training, stationary bike?

First of all, I own a $25 beater bike that I picked up from a garage sale a few months ago. It's an old(er) Univega Alpina Pro with wide (not sure if you'd call them mtb) tires. It's mainly for riding to campus (<1 mile away) and getting around town (not more than a couple miles).

I'd like to become a stronger rider, but am discouraged from taking longer rides because of the tires (I read in another thread not to regularly exceed 5 miles on mtb tires). Traffic is also kinda crazy in Berkeley.

Would I reap any benefits from using a stationary bike (the nearby dorms have a small workout room I can access for free)? Should I just try to ride (stationary) as long as possible? Other suggestions?

Thanks

I've never heard about not exceeding 5 miles on mountain tires. I know people who have ridden centuries on them. They are, however, not terribly efficient. You can find nice tires for your bike without knobbies, and that will remove that limitation, though they will likely cost more than your bike does...

On the traffic side, do some web searching to see if there are any resources, or ask at a bike shop. I also live in an area with a considerable amount of traffic, but there are routes you can ride that avoid most of it.

Now, on to the question about the stationary bike. Stationary bikes are okay from a fitness perspective, but most of them don't fit people very well, and they are - in my opinion - mind-numbingly boring. Having said that, with a book and some music, it may be tolerable, and it's not a bad way to get into better shape. Note that if the bike displays the number of calories burnt, it's generally wildly optimistic.

mileage limit on tire is until you see cords

for mtb tires, they lose racing freshness (knob ability to cut into dirt)
if you do too many road miles

in your case, perhaps you are riding just below racing conditions,
I'd suggest use those tires till they literally fall apart
you'll be fine

I ride the Lifecycle in my gym a couple nights a week after I lift. I like it, it has some nice hill programs and you can set the resistance pretty high. I can also listen to my Ipod and watch the TV's in the gym. I think it's a nice change.

i think you could reap some benefits on a stationary bike if you train right. perhaps keep a certain speed for as long as you can without your HR going too high, then the next time see if you can go longer, and just keep doing that, if it's one of those cool ones with the hill programs that can help too, if not you can just adjust the tension settings at random intervals. and the 5 mile thing on knobbies could be to keep the knobbies from wearing down, knobbies wear out extra fast on pavement, but on new knobbies i'd guess you could still get at least 1000 road miles on them. there's a used bike store in my area that sells used knobby and road-for-mtb tires for $10 a pair, and they are like new.