Alright, another newbie here...

Just starting to get into the sport at age 15 after finding a route to
the local bikepath in Rhode Island. Been riding one of those generic
wal-mart mountain bikes for the past few years. Half the gears don't
work and the ones that do can be fussy at times (like the lower gears
not locking in place as you approach a stop sign). One of the gears
is completely ruined as one of the teeth on it tore off, causing the
gear to tear in half (wow this stuff is made cheap). Luckily the
gears I use most often (7 and 5) work okay.

On the local bike path i've noticed people on what I believe are
called 'road bikes' (the thin tires). While I am struggling to hold
17mph these people, some looking in their mid 60s+ are speeding past
me. It seems whenever I see someone else on a mountain bike they are
struggling like myself. Are road bikes capable of faster speeds or is
it just the fact that I am just starting out and can't move that fast
yet?

Also, what type of bike would suit me best? - I ride on residential
streets almost all the time unless I am on the bike path (which is
paved as well). Just not sure how well something other than a
mountain bike would handle on the roads I have to go down to get to
the bike path - the shoulders are small and almost covered in sand,
gravel and other debris (such as the tar grit from the last hole the
DPW decided to dig).

Electronics... I have a garmin GPS which I wear around my neck when I
head out, but am wondering what other items there are that people use
while biking. The GPS has a handlebar mount but I am afraid of it
being stolen or damaged if I were to crash (took a corner too fast a
few months ago at an intersection and hit a steep curb - had the gps
been on the handlebars it would have been damaged).

What are the major differences between a mountain bike like mine and a
'road bike'? (Physical differences and how they ride/feel)

Is it better/cheaper to build a bike or to buy one pre-built? (And
what sites are there that sell bikes/parts?)

Not sure if I could build or buy a better bike with a few hundred
dollars but am interested in seeing whats out there (and building one
would be a nice project).


-Thanks for any help/info