Q: Power Mac G4 M5183-Can this computer be rebuilt with better hardware?

I have little doubt you will find lots of information by searching Google.

Which one of these 28 is it?

http://www.everymac.com/ultimate-mac-lookup/?search_keywords=M5183

Seems hardly worth the effort as it is officially obsolete and parts may be hard to find.

Obsolete products are those that were discontinued more than seven years ago. Apple has discontinued all hardware service for obsolete products with no exceptions. Service providers cannot order parts for obsolete products. These include ALL G4 models.

http://support.apple.com/kb/HT1752?viewlocale=en_US

With enough money and enough time you can rebuild and update anything. The question is: "Is it worth it?" which only you can answer.

In my experience, the Quicksilver and Digital Audio can be reasonably contemporary and up-to-date performers. Be prepared, however to keep a back up (working) machine and a parts machine available if you intend to rely on these oldsters, and keep a watchful eye and a few spare dollars handy as well.

Older than this - in my view - starts to come under the heading of 'hobby' and can easily become a money pit.

You've been warned.... now go for it!

Jon