Hello Calgal,

Picasa is currently End Of Life as of 2015, however it was an awesome program and is missed by many. You can get last version of Picasa from here. When I was testing Picasa today, I found that Google will still let you authenticate with their servers to download all of your synced photos if you have them synced.
If not you will have to either copy the photos over manually with an external hard drive. Additionally you can find out how to migrate everything including the database here.