How to create a partition for Solaris 10 from Ubuntu's installation ?
 

Also how do I create a shared partition between solaris and ubuntu?

Thank you !

You can use GParted partition tool (check/download here) in order to create some disk space for another OS installation.

You can then install Solaris on that free space.

Solaris has to be installed on a primary partition, so this could be a problem depending on your existing partition scheme. You can only have 4 primary partitions, if you need more partitions, then one of the primary partitions must be converted to an extended partition.
(The extended partition can then be split up further into logical drives.)

You can use linux fdisk or cfdisk to create your partitions, but you must know which primary partition you have created for solaris. You can then install Solaris into that partition. Solaris uses slices (up to 16 slices per partition).

Easiest way to share data is to create a partition that both linux and Solaris can read and write to. An example of a multi boot partition table is at the bottom of this page:

http://multiboot.solaris-x86.org/iv/3.html

Note that the extended partition is sda4 (last primary partition) and 4.1, 4.2 would be sda5, sda6, etc in linux naming conventions.