I'd suggest that you look at /usr, /usr/lib, /usr/lib/perl5 etc until you get to /usr/lib/perl5/site_perl/5.8.1/i386-linux-thread-multi looking for a file which is not a directory which it might try to overwrite. (It may be a messed up symlink.) When you find a possible offender, manually move it out of the way and then try the install again.

If you get the same error with a different directory, wash, rinse and repeat.

Then file a bug report with the Mandrake folks.