Welcome to the site! Unless you plan on changing out your brakes, I wouldn't bother changing the tires. There seeems to be incompatibiltity issues when leaving your existing brakes on a mtn bike and changing the wheels and tires(not in all cases, but most). Theres not a whole lot you can do to a mtn bike to convert it to road style. Your best bet may be to invest in an entry level TT bike, they go for around $1200. I have a couple training plans that I have used and written myself(sprint and 1/2 IM) that were very successfull, let me know if you would like me to send them to you. But basically, start out with a conservative distance and gradually increase to 3000-3500m total for your endurance swim. Remember to build, build, build, recover(in terms of weeks), and add speed/interval work into your weekly routine, this will later be turned into race endurance. Start out with short anaerobic sets(8x25 sprints) and gradually increase the distances, slow the pace, and shorten the rest intervals till you reach the peak phase, which by this time you should be performing a majority of your work outs at or near race pace. I also have a lot of experience with form/technique drills, so I can help there too if needed, good luck!

-Anthony

for what it's worth some generic training plans are available at trinewbies.com, trifuel.com, and beginnertriathlete.com but they are pretty generic

Thanks!!!!!!!!!