I wasn't too sure about the answer to this question ("So, where exactly is Kilimanjaro ?") and thought I would try and provide a brief overview, if nothing else, for myself.
Kilimanjaro is the highest mountain in Africa (hence the "Roof of Africa") at 19,340 feet or 5895 meters. It is located in north-east Tanzania near the east coast of Africa, on the border between Tanzania and Kenya (which is to the north of Tanzania). Another interesting fact is that it is only 205 km south of the equator.

Above is a simple graphic showing its location on a map of Africa, you can also check it out on maps.live.com or for an even more interesting view take look via the Tusker webcam.
Kilimanjaro has its own international airport and in terms of distance from the next really big city it is a 50 minute flight from Nairobi and 240km by road from Nairobi and 446km from Dar Es Salam.