I think the ide drive itself is part of the real problem. When trying the 7 betas out on an ide drive here I seup a temp dual boot of both 32/64bit versions and that was on the same cable as a cd burner I also have on. Simply having the HD slaved there saw no problems.

A bad drive or simply a bios setting change? At least you have 7 running normally on the sata which actually is good news for you!