Installing Windows 98SE after WinXp Pro... How is that possible?

Greetings!
Well, sorry to disturb you all, but I have a problem. I've got two hard disks. The first disk contains 2 partitions, and also the WinXp. The second HDD has only 1 partition. So, there's some more details: C: (Boot), D: <- Disk 1, E: <- Disk 2. And now comes the big question: How can I install a Win98 system when I have an other Win product (WinXp) installed? I had tried it, but my procedure messed up the Xp, and I had to reinstall, so I think it would be safer to ask you about this problem. Sorry if this question is too basic, but -as my name shows it- I'm a totally amateur dude.

 

take the drive with xp out format other drive and load it with 98 then put original drive back in it'll give you a choice of os