Thx for your reply.
I have been (and still am) in contact with ASUS' supportteam.
ASUS suggested me to change the BIOS SATA/IDE-setting to "combined" instead of "enhanced".
At the same time I discovered that I had used a 40-way IDE-cable and not a 80-way, which I therefore quickly replaced... and voila! ..now my dvd-drive works like a charm in Windows 7.
(I can actually even change the BIOS-setting back to "enhanced" and my dvd-drive will still work correctly in Windows).
However, my initial problem with a missing driver for the Intel Marvell IDE Controller still exist in Windows 7.
With a little luck, ASUS may find a solution for me, hopefully.
Otherwise my only "end-solution" would be to buy a SATA dvd-drive instead, because I fear that next time I want to do a clean reinstall of Windows7, then I still need to install WinXP x64 first due to the "missing" IDE Controller driver..
I must admit that ASUS bad decision to incorporate a cheap IDE Controller is just as bad as Windows 7 not being able to recognize an appropriate driver, when WinXP does the job perfect!?
...then again, we "gotta" keep the industry rolling by constantly buying new hardware, eh?..... sigh!