Im assuming that this sata dvd is plugged into the red sata ports, not white/orange? Thats weird man, but than for example my sata dvd is not shown in bios but works perfectly fine in xp32 bit(lol). I also see loads of posts from people experiencing the same issue as yours, but mostly on 64bit OSes(linux included). Dont know what to suggest really, maybe try that: unplug ide DVD, disable Marvell IDE in bios, switch sata configuration back to IDE, than try again.
Can you boot from the sata dvd though? Did you try to reinstall vista using the sata drive?
I took a chance and went with a fresh OS install and the sata dvd drive so far is being detected in windows. Solved my own problem, seemed to be something in the original vista install that was the problem