You can install XP on a seperate partition on your hard drive and dual boot, in order to give yourself plenty of time to re-install your programs from Win98.
XP has a boot manager in it, but I would reccomend creating a seperate partition and changing the active primary for the install, this way you could wipe out Win98 without problems when you are ready. Partition Magic has a good boot manager for doing this.
It is a very bad idea to install XP over Win98, you will be plagued with problems. A clean install is the only way to go.
Good Luck.
