98 days to get myself rockin'

I posted this over in misc.fitness.misc but didn't know there was a
specific walking group here as well .... I just figure maybe its better
targetted here.

I have 98 days to get myself into some kind of shape. I am headed off
to the Grand Canyon with some friends for some camping and hiking --
and its the hiking that is a little intimidating as it'll be hot, I'll
be carrying a pack and I just quit my 20 a day smoking habit two days
ago.

Despite my relative size I have always been able to move about - my
goal is to not slim down much before the holiday even though I need it
but to build as much stamina, lung capacity and heart strength as I can
between now and then. I have switched to a solid diet, and I have the
time to hit the gym every night of the week (although I won't).

I wanted to see where I was tonight and as the treadmills where kinda
busy I hopped on an excercise bike and continually raised the
resistence till my heart rate was nicely in the center of the cardio
zone on the machine --- this got me to thinking .... presuming I did
some form of cardio every day, if I kept my heart rate within the zone
presumably the intensity of my workouts would increase to reflect my
growing fitness ...

.... is this going to be enough to get me from my currently low stamina
out of puff state to a point where I can at least complete a few hours
walking up and down hill without having a miserable time?!

I am 29 years old (I'll be 30 when I holiday)

6.2"

266lbs (I reckon without starving myself I will remove at least 30lbs
over the next 14 weeks -- I really drop weight fast, I just eat log a
hog mosta the time and there is a lotta muscle in there as well)

Whats the best way to build legitimate endurance in 14 weeks?! -- ever
increaing lengths of workout or by sticking to a set time and
increasing the intensity?! I was really just thinking of walking and
walking and walking .......