OS Downgrading

Can anyone help??
Have an HPVectra loaded with XP OS..
I want to install Win98 OS.. 4 reasons not needed.
I format the drive and repartition to FAT32 and reload Win98. The OS load is successful and there are NO errors, but when the the machine boots for the first time it says Win98 is running for the first time and then goes to “safe mode”. When I choose “safe mode” it reboots and loops to safe mode. I have tried several times using different techniques and different Win98 software and the result is the same. I can retro to Win2000 without a problem, but not to Win98. Is there something I need to do on the BIOS? or file formatting on the drive? Anyone got any ideas or had this problem?? Is it a hardware incompatability issue?
Thanks