Ok, I'm still learning this too but here's a quick guide to the numbers. First, by default your memory timings are probably configured by SPD, which is like auto-sensing. Usually you will get reliable, though maybe not very quick timings from SPD. To put in your own values there's probably something like 'Override SPD settings' or similiar in your BIOS and once you hit that you'll get some options.
My system is 2-3-3-6-1 where:
1) CAS Latency ? 2
2) RAS-to-CAS ? 3
3) RAS Precharge ? 3
4) RAS Active to Precharge (Bank Cycle Time, tRAS) ? 6
5) Command Rate - 1
Check your BIOS to see what it calls each of these values... it seems to be different depending on your vendor and BIOS version. Then go to your memory manufacturer's site and check their specs. My memory is Corsair XMS 3200 and here's what Corsair suggests for this memory:
Testing parameters for XMS3200 CAS 2:
CMX512-3200C2 Data Sheet
CMX256A-3200C2 Data Sheet
Motherboard make and model: EPoX EP-8K3A and/or Asus P4S533 and/or EPoX EP-8K5A
DRAM Clock: 200 MHz
DRAM Timing (overrides SPD values): Manual
System Performance: Normal
Bank cycle time (or tRAS): 6
Bank Interleave: 4
RAS Precharge (tRP): 3
RAS-to-CAS Delay (tRCD): 3
CAS Latency: 2
Command Rate: 1T
Memory Voltage: motherboard default*
Anyway, that should get your started.