needa boot into 98 with disk

ok heres the setup, i got a computer with 2 operating systems linux and windows xp, i also have a hotswappable drive which is H: in windows xp. now i have a hard drive with windows 98 in the swappable drive, now i need to be able to boot windows 98 so i can get to dos and run some forensic tools. now i would like to be able to boot it like i do with linux which is with no boot manager and i just throw in a boot disk and the computer boots to it. so when i throw in this disk it boots to 98 but when disk is not in it then it just boots to XP. please help , keep in mind i only want to boot to 98 when disk is in, i asked this somewhere else and i got alot of responses about bios and some other stuff. thanks