If you want to reinstall Win98 but want to keep WinXP, you need to backup these files Boot.ini, NTdetect.com, Ntldr and Bootsec.dos (if applicable) in Root sector (C:, usually in Win98 partition).
Boot your comp by Win98 setup disk, and type at DOS prompt "sys c:" (w/o quotation marks) to overwrite WinXP bootloader, reformat Win98 drive and reinstall it. After Win98 has been installed, Boot your comp by WinXP CD, and at its setup menu, choose <b>Repair</b>. It will ask you for administrator's password. When it's at Prompt, type <b>Fixboot</b> to repair WinXP's bootloader (Remember to copy all files boot.ini, etc that you backup earlier back to where they are before) then restart.
Good or Bad have no meaning at all, depends on what your point of view is.