Greetingz!
A Word About Sun
Well, a Sun Ultra 45 runs an UltraSPARC-IIIi CPU, this is wildy different than your standard x86 CPUs manufactured by Intel and AMD.
Ubuntu & SPARC: The thrill is gone, baby...
Back in August 2010, Ubuntu stopped supporting SPARC (and IA64) CPUs (see
here). The last version that might work for you is Maverick Meerkat (10.10).
Virtual MacOS: Apples & Oranges
There's quite a few 'hackintosh' type articles out on the Internet. Be warned that most involve downloading a customized MacOS ISO, and there's limited functionality at best.
Google is your friend.