Solaris has its own package manager. Read the man page for 'pkgadd', 'pkgrm', and 'pkginfo'. If you want to install something that didn't come with Solaris, have a look here:
http://www.sunfreeware.com
There are pre-compiled packages there for almost anything you could want(a lot of things you would take for granted from running Linux). A few sites on the web will have Solaris binary packages available for download, but it isn't as common. If you're not comfortable with downloading and compiling programs from source code, now would be a good time to learn.
Also - yes, you can get the RPM package manager for Solaris -- but as previously stated, you won't be able to install and run precompiled Linux binaries by RPM. I guess you could use it to install source RPMs, or use it to create&install your own Solaris binary RPMs, but it would make a lot more sense to just create&install Solaris packages instead(pkgmk).