Windows vista minimum free space requirement

i want to kow the minimum free space requirement for windows vista windows vista upgrade advisror told me that u required minimum 15 gb harddsik and 40 gb is good so what is ur experiance ?

I think a minimum of about 20GB is absolutely necessary. Other than that, for updates and future service packs, 40GB sounds good enough. :)

My Windows folder is using 15GB, Users folder is 4GB.