Step 5 of install fails

[Doug]

When I get to step 5 of the install (Ubuntu 10.04 or 10.04.1 for 
Desktop-i386) there is supposed to be a way to select a partition, but 
it doesn't work.  The only option is to wipe the disk.  I want to 
install to an extended partition,
/dev/sda9, which starts at 10761 and ends at 14075, and is formatted 
type 83, Linux.  It is otherwise empty.  On this machine there are XP, 
PcLinuxOs, and Debian Squeeze, all accessed by Grub, and they all work.  
How can I add Ubuntu to the stew?
Thanx--doug

-- 
Blessed are the peacemakers...for they shall be shot at from both sides. --A. M. Greeley