Now, for the initial installation of Windows 7 x64, I had not plugged neither the Hitachi HDD nor the XFX 5770 in. I loaded it up, installed all drivers and everything seemed to be working fine.
Then, I installed the HDD and the discrete video card and the troubles began. After installing Catalyst 11.6, some applications simply started crashing when I tried launching them - for instance MSN Live Messenger and Steam. Also, flash doesn't seem to work at all - it simply crashes in Firefox 5 when I try to view a video on YouTube, for instance.
I tried uninstalling the Catalyst driver and everything worked fine once again. I also tried using Catalyst 11.5, but with the same result.
I also had some issues installing the Eltron 3.0 USB Driver - everything simply locked up in Windows when I tried to do so. I have since disabled USB 3.0 in the BIOS as I don't have devices that make use of USB 3.0 anyway.
I have run a full pass of memtest86 and about half an hour of prime95, both of which gave no errors.