Flights & getting there
The easiest and most practical way to get here is to rent a vehicle. The roads are good enough that a 4WD is not necessary, unless you plan on exploring a lot of the parks. Even then, most of the lodges inside the parks can organise group drives.
The major routes are well served by buses and matatus (minibuses) and it is fairly easy to find cheap transport. However, if you are short on time, this might not be the best option as you are at the whim of the driver, as well as your fellow passengers (particularly if there aren't many!).
There are regular flights from Nairobi to Nanyuki Airport (US$130, 40 minutes) and small airstrips in most of the parks for charter flights.