EDU Buys Used to Offer 4 year Apple Care
When I purchased my G5 Dual 500 MHZ Powermac there was a 4 year Applecare available. I don't know when that was dropped.
If you want a 4 year warranty, purchase both your computer and Applecare with a credit card (preferably AmEx) that doubles the manufacturer's original warranty. The 4th year mirrors the 1 year original warranty and will be covered by the CC company.
When I purchased my G5 Dual 500 MHZ Powermac there was a 4 year Applecare available. I don't know when that was dropped.