Mandrakelinux 10.1 (Community) appears to include RAID support. I know you are trying to install Mandrakelinux 10.0, but maybe this will help. Also, Mandrakelinux 10.1 (Official) is scheduled to be released 10/15/2004. You should see it on the ftp mirrors by the end of October.
You can see the release notes
here
The part on RAID is a little way down the page.
HTH,
