Ram configuration, what would be best???

My newer computer died and I'm now using on older HP Pentium 4 2.6ghz with a 478 board, don't laugh.

The board supports ddr400 and dual channel and has four slots. I have a whole whack of differnet rams and timings and I'm wondering what amount and configuration would be best

I have

1 stick of Kingston 512mb ddr400 Cas3

3 sticks of generic 256mb ddr333 Cas?

should I just put all four in there or should I use two slots for dual channel. Does the extra ram offset the performance increase of dual channel. Will 512mb in one slot and 256mb in another run in dual channel, so many questions so few answers

Any advice would be great.

Will all my timings be reduced to my lower ram?