Memory timings...

[lazer_viking]

Is there some sort of set memory timing rules you have to follow? Because the only timings settings I can get to POST are 3-3-2-8. I noticed 3-2-3-8 didn't work when I did it by accadent, so I concluded the third number can't be higher than the second number. Then when I was trying to overclock and I wanted a little more speed out of the RAM, I relaxed the timings to 4-4-4-8. That didn't work either (two long beeps, then a restart before even seeing the motherboard's splash screen). Then I tried 4-3-2-8 (same as stock, except the CAS is one higher) and that did the same thing as 4-4-4-8. So I don't know what to try now... anyone know what timings I can try?
edit: i have OCZ platinum PC4000 stuff. im trying to get it to DDR540.