Slave Drive

If I have Windows98/se for my mane drive and I want to put in a secondary Drive in, And I think it might have windows 2000 or XP ON IT,Or it on it at one time.Will it cause a conflick with the two systems.I was told it has a nfst or something like that on it and windows98/se does’nt.Will it keep the second drive for loading up.It seems like it reconizes it but it would not give it a drive letter.I have some music on it I want to retrieve .