new biker

Question
I have a mountain bike. However, it was my mom's. It is good condition, but I am worried slightly about fit. I've spent this last semester at college training on a spinning bike with a different set up. I guess I am confused as to whether these differences really mean anything and maybe I just need to get used to it. On the spinning bike, I was instructed to pull back the seat more and my body was more horizontal to the ground. Whereas with my mom's bike, my legs feel almost behind me, and the handle bars are entirely horizontal. The spinning bike had horizontal/vertical handles. I'm sure you know what I'm talking about. Most road bikes with thin tires have this type of handle. The handle are different but even if I go horizontal, my torso is too long to do this and I have no where to place my hands. I just started a job in a very biker friendly area,  and I plan to bike 20 miles to work every day. I haven't started yet since I just started a few days ago and I need to find my way around the area. I don't have money to buy a new bike, but I could put 50 dollars into it if you have suggestions. I know that I can get the handle bars changed (right?), but I don't know how difficult it would be to get the handle bars placed so that there was more room. I'll be biking mostly on paved trails to work. Is it ok that I'm using a mountain bike wheels or do I need to get road tires. Someone told me that it is not a good idea to do road biking with mountain bikes. To be very honest, I know very little about biking. What do I do?

For background info. I'm a 20 year old adult who is a runner and a swimmer and a very new biker.

thanks!
Christine  

Answer
WOW,
Congrats!...Thats' the longest question I ever recieved LOl. Just kidding.

Okay here we go...um, spining bikes are designed for comfort, not to move. So you will not find a bike as comfy as a spining bike.

Secondly, What size frame do you have now and how tall are you? (sounds like a dating sight now)hahah.

Thirdly, Get a TORSIONED Handle Bar (the wavy one) with a rise (some people call them RISER BARS also.

Forth, If your only biking on paved trails get SEMI SLICK Tires. Also get them 26 X 1.50 (that means they are narrower and will go quicker!