Ok, since you have clear the Charity doubts, hmm, Ben Nevis and Kilimanjaro.
firstly read this 2 pageshttp://www.summitpost.org/ben-nevis/150801http://www.summitpost.org/kilimanjaro/150202
Having done so, now formulate the climb.
Which route, what type of climbing partners, how much you plan to spend, when you plan to climb as well.
If climbing the peak is the only goal, then congratulation, the easiest path of both mountains are not technical, and occasional use of hand to grab some ropes is what you need.
An inexperience climber may face tiring, breathing difficulties and cry on the mountain, but seriously if you prepare well enough, there isnt any real big deal.
the only main concern for your life is the attitude sickness on kilimanjaro due to its height, so you need to prepare before hand, buy some diamox and do a lot of cardio.
train your stamina, you need climb a lot of stairs, run a lot, and do a lot of trekking.
try to train at least 5 days a week, trek along the hills near by, try to run a long distant (start short, and slowly increase the distant covered)
the simpleast route on Ben Nevis is Pony Track, and there is no real challenge if you are prepared enough.
For kilimanjaro, you just need to do enough traing, probably with weights added on your backpack, and do some camping..
try doing multiple days hiking