DO you mean simultaneous writing of identical content, or just simultaneous writing of different content to each drive? I regularly run three different drives simultaneously (Yammy CRW-F1, Plexy 40-12-40, and Litey 40-12-48) to write different, or identical, content to each drive. All I do is:
1) open Nero and select the first drive
2) open ANOTHER instance of Nero - it'll ask you to choose a drive again, but the one you chose first will no longer be offered to you, so you choose one of the remaining drives (in your case, it'll be the only drive left, cos you have only 2 drives on your system bus anyway).
3) obviously, if you have another drive, you repeat step 2, but this is irrelevant for you.
4) now, if you want to write the same data to both drives, simply use one of the Nero windows to create your project, save the project (you don't need to save an actual image - just a project reference file is adequate), and then also open the project in the other Nero window.
5) simply tell each instance of Nero to get busy burning to the drive they are 'connected' to!
Admittedly, this is not quite the same as TRUE simultaneous burning, like in a cCD-copying tower, using Padus Diskjuggler, but the end result is the same, so gives a damn? (and you do not have identical drives anyway).
I find that with three drives running simultaneously at 44x, 40x, and 40x (and even with DMA enabled on both EIDE buses), my P4 2.xx ghz does tend to struggle as they all approach the outer portion of the disks being written (which is where the data transfer is fastest, obviously), but BurnProof takes care of this, and I have honestly not produced any coasters running all three at the same time.
Try it!
CDrZeus