Can't install Mandriva

[dwarfer]

Hi all, I'm trying to set up a triple boot system with XP, Vista and Mandriva linux. I have already installed XP and Vista onto 2 seperate partitions and am trying to set up Mandriva on the 3rd which has been formatted with the ext3 fs. When I try to install Mandriva I select use existing partition and select the ext3 partition, it thens says formatting and then goes off and won't continue to install.

Thanks.