Sun Studio 11 is currently available only as a product that must be installed via Solaris packages, and you need root privileges to install it.
If you just want to try out Sun development tools (as opposed to creating production software for release), you can get the Studio Express version. Studio Express is a preview of the next release, updated every few months. The download is an installation image that you can put anywhere. You can't patch the image -- to update it, you have to install a complete new image. You can find more details here:
http://developers.sun.com/prodtech/cc/downloads/express.jsp
You can install studio 11 without root privilege, but it requires playing a bit with fakeroot and the -R option of pkgadd, so I would not recommand it if you are not familiar with this kind of hacking. Since it means installing the packages "by hand", you can also select which to add or not to add. The compilers are (at least they seem to be) fully relocatable, so you can install them anywhere.
The express program may be an option, but it is not supposed to work on solaris 8 :-(