You will get the "press F1 to retry boot or F2 to enter system setup" message. you would need to format and partition the IDE drive then copy your boot.ini osloader and 1 other file for NT to be able to boot, or use a fault tolerant boot floppy. Microsoft technet should have articles that details how this may be done. you may have to edit the boot.ini as with the addition of the IDE drive the logical partition of the O/S will have changed.
Because of this, your system reliability is lower, if EITHER disk system fails, you will not be able to boot. That is why Dell does not recommend that the systems be operated with a mix of SCSI and IDE drives.