put a clean floppy disc in the comp and Double click the download file it will create a boot disc. then start the comp with the disc and at A:\> type format C: so it looks like this.
A:\>format C: follow instructions you do not need a label at the end of the format. then restart with floppy disc and choose start with CD-ROM support, I do not know what Your Drive letter was but if it was D:\ it will be E:\ it moves up one until you have windows loaded so after you get to A:\> type X: the X being you drive letter then when it as changed to you CD drive put the Win98 CD in and type setup and press enter follow instructions on screen
If your XP system is formatted with NTFS instead of FAT32 it will be more complicated. If you look in My Computer at the side of your drive it will tell you the file system employed on each drive, if not click at the top and enable 'File System'.