I'd use 2 x National LM324AN quad op-amps (or similar) to isolate and condition the photosensors. You
will use 5 of the 8 available op-amps as voltage followers (buffers). I'm assuming these are
CDS (Cadmium Sulfide) photoresistors.
Here's a picture of one sensor. The output of the op-amp goes to an analog input on the ATMega8.
The way I've wired it, you will get a low A/D value in darkness, and higher values with more light. You can
try different values for R2, from about 2.2K up to 1M Ohm.
By using a separate op-amp for each photosensor you should get good isolation between them.
It is better to place the op-amps as close as practical to the photoresistors, and run relatively long wires
from the op-amp outputs to the ATMega analog inputs rather than have long wires between the photoresistors
and op-amp inputs. Best of all is to use short wires everywhere, if possible.