Last week I tried to post an update of my situation but this site was temporarly unavailable. But now I'm here. So... this is what happened:
I tried installing Win7 x64 on AHCI mode on my Vertex 3 120GB SSD for about 3 times. Every time Windows got back into the install after the first reboot while installing the installation got stuck and the computer came into an endless reboot circle. On that point I set my BIOS settings back to IDE mode and it seemed that the installation could continue in IDE mode. And that was just something I did not wanted because of the limited performance of a SSD on IDE mode.
BUT, and there is the big but: while struggling in this proces my BIOS didn't recognized my SSD at all times. And that happened more and more. I fixed this issue a couple of times by resetting the BIOS by powering down and removing the battery but that went quit irritating after a while. So I contacted the manufacturer of the SSD and send it back for RMA. I mentioned that I lost my patient on the Vertex and asked for changing it into a Crucial M4 128GB. That was no problem for them and 3 days later I ran Windows 7 x64 on AHCI mode on my pc without any problems.
So in the end... OCZ Vertex still sucks
Thank you all for all the help.