solution
Yes it is. But Win XP is on NTFS partition and Win98 on FAT32 (AFAIK). When you want to have multiple systems on your computer, the best solution is boot manager. Your harddrive is logically divided into multiple partitions(logical disks(drives) as you can see in Explorer(My Computer)) or there is only one NTFS partition (default - after default Windows install without manual change to disk during installing XP(throug XP setup) or through third-party software like "Partition Magic" or simpler built-in fdisk(on bootable floppy drive for example)). Here is an example:
You have 30GB harddisk. Default state is that your harddisk are clear, no partitions created. We decide to devide it to three logical drives "C:"(system drive(WINXP),partition type(NTFS),state(ACTIVE(bootable)); next drive "D:" is dedicated for data for ex.(type FAT32(if multiple systems installed it's good to make data drives to be of this type-is visible for WIN98 and WIN2000,XP,...;when you made it NTFS only WINXP will see it.),state of this drive is default after creation = NOT active="bootable"). The third partition can have same parameters as the second one. This drive is for backup-ing for.ex.
OK, now we have 3 partitions with WINXP installed(on the first "C:"drive (partition)) and two another disks D: and E: for data (first partition of size 10GB and second and third of 5GB = 20GB total(10GB free on physical disk(for new installation of WIN 98))
Now we create new partition of type FAT32(Win 98)of 10GB size(all free space).Don't set this as active(active - means actually booting(you cant boot if there is not system). But if you want to install on it select this partition as ACTIVE(there can be only one partition ACTIVE at any moment). Restart your comp. and you will see message that no system found on disk(because there isn't

. Change boot sequence to boot from CD drive as first drive to run Win98 setup and install 98's. Congratulation, now you have two systems on disk and on XP you see c: drive(XP), D

system drive of Win98-drive letters was changed- THIS DRIVE WILL BE NOT VISIBLE IF BOOTMANAGER IS USED) and E:drive(original "D:"-data) and F: drive(original-"E:").In Win98 you will see only your C:, plus D: and E

system drive of XP will be not visible because WIN98 can't see partitions(drives)of NTFS type).
Now you always boot to WIN98(because that partition is active). Now you have to run some type of BOOT MANAGER software. "BootEasy BootManager" is good. There is more bootmanager software. You install it by booting to dos from floppy(WINDOWS/DOS booting floppy) and run that software from other floppy(or on same floppy). This sofware do not require installation it change booting (hardisk MBR-"Master Boot Record",etc.). This software makes two important things(if allready set). You simply choose from menu which system to boot.(which partition will be marked and set as "ACTIVE" - THIS DOES bootmanager, it is one of it's purpose. The other one is that you can set which drive you can see in each state(booting XP or Win98). For example you can disable(make HIDE funkcion)on partition on which resides win98 if you are booted in XP - then you will see only C:,D:,E:.( as in win98 default).
I don't tell you how exactly in boot software set this(it varyies). You will find it. But try it on testing version of computer ;-) for the first time. This is a little advanced configuration of PC and you can delete your system drive or corrupt partition by misstake.
P.S. If you want to reinstall system or format system drive ALLWAYS remove bootmanager and set active that partition to which you want to boot from.
I hope that you understand this and I recommend you to read more documentations about this. (This, what I wrote is a very good start - there are only few specialities
This is advanced thema so sorry for my "shit" english ;o)
Morb