mixing memory issue 667Mhz and 800Mhz

The 3 beep code means a problem with memory. Perhaps your system does not support having both ECC and non-ECC memory installed.
Perhaps the Geil does not work fully correctly in your system. Test this by downloading and running memtest86+ through at least a few complete cycles.
Also, try all the different possible combinations of the 4 DIMMs in different slots.
Perhaps manually setting memory bus speed and latency settings will help. I would also contact Geil tech support and ask for their help.

[/img]The memories work fine on their own .
So the 2x512 work fine and the 2x1G work fine. I used memtest86 Plus for this.

I tried all possible DIMM combination (DUAL and NON-Dual) and everytime I pair the 512 with 1G the beeping appears and nothing can be done.

The BIOS is stupid enough to be very simple and has no ECC disable/enable settings. The motherboard has no specifications and I can only learn it's HP model 06A68h which means nothing and cannot find any documentation related.

I don't know if I can do anything at this point rather than to throw away the 512 DIMMs or try sell it (which would be a fair price ? )

Andrei.

you could sell the paired dimms of ddr2 ecc for quite a bit i believe..

That might be the best. The problem with selling ECC, but unbuffered, DIMMs is that there is not a very big market for them. Standard 1GB DIMMs sell for around $40-50 each these days, so if you could sell your ECC 512MB DIMMs for $10 each, I think you would be lucky.