Ram question

[Rifter]

Ok, i am building a new computer and i have 4 sticks of ram and want to use them all. The ram specs are as follows:

2x1GB Corsair XMS2 DDR2 800 4-4-4-12 2.1v
2x2GB Corsair XMS2 DDR2 800 5-5-5-18 1.8v

Now before you tell me that the ram voltage differance is the problem i have tried the 1GB sticks at the lax 5-5-5-18 timings at 1.8V and they will pass memtest as singles and together. The 2GB sticks also pass memtest fine. However when i put them all in together memtest will fail badly, even if i up the voltage to 2.1v it still fails. Im trying to run them all at the 5-5-5-18 timings. The 1GB sticks by themselves work fine and so do the 2GB sticks, im pretty stumped any suggestions?

Systems specs as follows:

AMD 7750 kuma
Foxconn A7DA-S
Sapphire 4830 512MB
Seagte 7200.12 500GB
Samsung SH-222 IDE 22x burner
Arctic Cooling 550RF PSU

I was running the memtest from a linux live CD im currently installing 64bit vista and will dual boot it with Linux Mint 6 64bit.

 

[GhislainG]

Try looser timings, e.g., 6-6-6-21 to see if it helps. Getting 2 kits of very different memory modules working together can be very challenging.