2 os on same computer

Its a completely manual process in your case. If you windows xp is in a different directory then your windows 98 (Should be or an upgrade would have been done) then you can remove your windows 98 directory. you should be able to tell you xp directory by being in windows xp and issueing echo %Systemroot%
Use the search/find to find Command directory. That is your windows directory, you can remove this and its parent if you no longer want windows 98 on your system. Since 98 and xp share the program files directory you may not be able to remove anything in that directory. Only a skilled person can tell what should and should not be in that directory. IE, if you knew in windows 98 you install Mcafee, but your windows xp is using Norton, there is a really good chance you could remove the Mcafee.

Look at the file on your computer on the root of the C Drive, The file Boot.ini will tell you where exactly everything is. This file is probably read only and hidden. View the file in explorer. In it it will tell you were the windows directory is. If it matches your windows XP directory then your workstation was upgrated and you can then massage the boot.ini file to remove the windows98 option and put the default option to be windows xp. http://www.osr.com/ddk/ddtools/bootini_5qer.htm is agood article on how to change it. Then my first article should provide more info.