Then try to create the partitions with fdisk or cfdisk instead of the Ubuntu installer.
Unless special needs I would do this:
- create a first partition for /, type 83 or linux (12 G)
- create a second partition for swap, type 82 or linux-swap (1 G)
- create a third partition for /home, type 83 linux (remaining space)
Then you could use something like mke2fs or mkreiserfs to create ext3 or reiserfs file systems in the linux partitions but I guess the Ubuntu installer can do that for you.
To know more before proceeding you can search the Internet for 'man fdisk', 'man cfdisk' etc.