Fly to Nairobi - Jomo Kenyatta International Airport. Many nationalities can buy a 1 month toursit visa on arrival. Check current details on the US or British Govt websites. http://www.fco.gov.uk is a good start. Make sure you have got all your inoculations up to date, a supply of malaria tablets (although i dont use them at altitude anymore) and your own medical kit with sterilised needles. Healthcare is available but you dont want to have to rely on it up country. Get good travel insurance with at least 5million USD of medical cover including repatriation cover.
Your first time in Nairobi you should get someone to meet you at the airport unless you are an experienced africa traveller. If you dont know someone then book a reputable hotel in advance and get a taxi. Check the current price so you dont get fleeced and take a licenced cab. They are pretty good from the airport. Spend a day in nairobi getting your bearings in daylight. I wouldnt advise trying to run though. Get a decent guide book with maps so that you can find bus stations etc.
From Nairobi you have three main travel options.
1. Travel with someone you know by private car
2. Travel by bus - Kenya Bus, Akamba and others run several buses a day from Nairobi to Eldoret.
3. Matatu (a minibus taxi) not recommended on long journeys as they have a poor safety record. The bus stations are easy to get to and pretty safe by african standards. Tickets can be bought on the day for about 5 USD. Enbglish is widely spoken
From Eldoret you will need to get a matatu to Iten (about 45 mins and 2 USD max). They go from the junction of the main road with the Iten Road. You could just pitch up in Iten and get dropped at the High Altitude camp run by Lornah Kiplagat. Its about 25USD a day. From there you can find who is training and when. Just ask around.
Other training camps in range of Eldoret are at Kaptagat. Camps change locations fairly frequently.
Internet is everywhere and very affordable if a bit slow outside nairobi. mobile phones - if you have a GSM phone you can by a kenyan pay as you go sim card for less than USD
Security: you accept a higher level of risk in everything you do - travel, food, personal safety. But with basic precautions it should be no more dangerous than inner cities in north america or western europe. So the precautions are: be aware that your first 48 hours is your highest risk because you stand out, dont look rich - so no jewelry or flash clothes, dont go out at night, make friends with kenyans. Ultimately this gives you a 99% chance of being OK. People like Ondoro and Paul were specifically targetted because of their known wealth. But then rich guys in nice cars get shot at and robbed in our countries too.
To enjoy a trip to kenya you have to appreciate that things move much slower than in the west, 'arrangements' can change at the last minute, time keeping is poor by our standards. If you are in western mindset you will get quickly frustrated. Chill out, get into the pace of life and live like a kenyan.
On a running note: take it easy until you get the measure of the altitude.
Make friends, stay chilled and you will have a great time. And remember its africa and things can change very fast so never get complacent.
This is starting to turn into a guide book so i'll shut up now.