ACPI? ACHI? Well... each of us were wrong! xD It's AHCI ! xDDD Thx for pointing it out! :)
So for the question: It's like an onboard sound card: If you have it turned off in the BIOS, the windows won't install the driver, cause it can't detect it. Now imagine you have an onboard RAID: If you turn it on, windows won't see the hard drives as it did before. But in the other hand, if you install win on RAID mode, if you turn it off, it won't see them. The trick is to set AHCI or standard IDE or RAID before you install windows, and keep it that way, so it will install the appropriate drivers and will be able to boot.
What I did exactly was that I enabled AHCI (and disabled IDE as a result), and I wasn't able to boot. So then I disabled it back, googled it, and found out, that I have to install the drivers manually, before I set it, or else they won't bee loaded at boot time, and the windows won't beet, so it won't be able to detect the "new hardware". Instead 'cause my win install was an old crap, I backed up my data, enabled it, and reinstalled a new win. This way I didn't have to mess up the drivers, and I even cleared up my old mess, while switching to x64.
About setting x64 you're officially right, but it has a great advantage: Win7 has a bug, most widely known when the network disconnects randomly. It's because there are programs like Bonjour and Chrome that messes with the network drivers (TCP stack namely). After installing these, if you reinstall the network driver (or install vmware that does this), it will install some bad stuff (randomly, not always, it's a bug after all). To fix this, you uninstall programs, reboot, delete network drivers, reboot, and let the win install it back. But not with x64, cause these programs are x86, and they will have separate stuff on a x64 system. This is the main reason I switched to x64, cause I'm experimenting with vmware, while having chrome and bonjour installed. It works.
Now, just imagine, if this bug is not restricted to the network drivers, just they are the most often reinstalled ones. You even get lot of google hits claiming this is a wifi-only bug, because wifi drivers are the most often reinstalled network drivers. This could easily be the case with my IDE drivers, causing the system hangs. Just a theory... It's up to you all to sort out which one helped, I don't have the bug anymore! :P
Here is my story, hope now you understand, and it helps. I love you all! :)