In a nutshell, what is the fight over in Georgia all about? Is there a simple summation as to why Russian tanks have rolled into the area? I don’t mean to enter into a debate as to whether or not Russia is justified or if this is a good idea or not. I’m just curious as to what the issues are? What do the Georgians want; what do the Russians want; and what does S. Ossetia have to do with any of it?
I suggest reading the thread in Great Debates on the conflict; amongst the discussion of the value judgments involved can be found some specifics about what is going on, and why. 
The thread is titled something about Russia wanting an empire…
Also, the Wikipedia article on South Ossetia has a reasonably concise explanation of the history of the area and the desires of each of the parties. South Ossetia - Wikipedia
OK so its complicated…
Russian point of view - Georgia is oppressing the region, which has a pro-Russian majority, and it rightfully fought against Georgian rules, and won de-facto independence in 1992. On the 7th August Georgia sent troops back in to Ossetia force it back into Georgian rule, in the process causing terrible civilian casualties. Their intervention is no different to western intervention in Kosovo or East Timor.
Georgian point of view - This is outright invasion of Georgia by Russia, and South Ossetia is just an excuse (think Sudetenland). Russia is just flexing their muscles and is mad at Georgia because it is pro-western. South Ossetia is Georgian, and their recent actions there were perfectly legitimate police actions in their sovereign territory.
Irregardless of whose position you agree with, recent actions by the west in places like Kosovo, and East Timor (not to mention Iraq), make it pretty hard for the west to take the moral high ground and condemn Russia (esp as the Serbia and Indonesia said exactly the same things regarding Kosovo and East Timor as Georgia are saying about South Ossetia).