what is your computer system that you are going to dual boot from and install dsl to the sd card? Particularly, how do you connect the sd card to the computer and will your BIOS allow you to boot from the sd card or not?
DSL can be installed in 50MB, so you have plenty of space on the 2GB drive. For an initial test installation, you can try one partition and set it as bootable.
> man fdisk