I guess you can, but it is unsupported.
You will probably need to un-install oracle 9i, install Developer, and then re-install the database client software.
U can install D2k by changing home path of oracle 9i. while installation of D2k it will show home path of oracle 9i which already loaded in u windows XP by changing ora_home path u have to change installation path also. U can use on windows xp both oracle 9i and d2k