How to train?

I have signed up for the sundown 42km.
The next question- how do i train for it if my target time is 4:30.

I sort of favour the 3-runs-a-week training schedule, which leaves me time to do other things.
Not forgetting project Haley is to be kick-off in March 09.
However, I wonder whether the mileage is enough for me to accomplish a sub 4:30 marathon.
I guess I will put it to the test.

Here's likely what i will do
1. 2 cross-trainings a week, with weights targetting lower body and core strengthening.
2. 3 runs a week- 1 interval/hill alternate, 1 tempo run, 1 medium distance/long distance alternate, with marathon pace built-in.

Lets see how the training progress before i make any modifications.

All thoughts and advises are welcome.