ok, simple answer.....
you pay the insurance company $X every month.
When you take your dog to the vet you pay them in full.
You go home and submit a claim to the insurance company...
They have certain guidlines they follow to decide if you are re-imbursed.
If its a yes they send you money back, if not, you payed the vet bill alraedy.
existing contitions are not covered.
My cousin had insurance for her cats through-
http://www.petinsurance.com/groups.cfm?ec=N343
I have no idea how much she payed. The website though tells you what plan options they have and how much will be re-imbursed for each type of care. The basic plan does not cover yearly exams.
A quick quote on Kino, My Samoyed came out to be about $34 a month.