Technically, you should be able to run Solaris 10, OpenSolaris based distributions and Solaris 11 Express on a SB100. However, low end SB100 have 512 MB of RAM, not enough for the installer to complete successfully.
In such case, you might install
milax, a lightweight OpenSolaris based OS. The bootable CD doesn't seem to be downloadable any more but there are wanboot images
here.
In any case, here is a useful SB100 FAQ:
040.digital-bless.com: Unofficial SUN Blade 100 FAQ