One world XE demo installation fails for second time

[JDdev]

I installed JDE demo successfully for first time but unable to reinstall ( though i have removed it from Add/Remove programs)I tried even with regedit by deleting some of the files but still i am unable to re install. If anybody can suggest something on this it wud be of grt help

Note : it happened same with different systems I am able to reinstall only if In reload my OS windows XP.