planned to install cs3 and then purchase the upgrade and install that.
The only upgrade path to CS6 is from CS5 or CS5.5.
CS3 and CS4 became ineligible to upgrade to CS6 on Dec 31, 2012.
Your options:
- Buy a new version of CS6
- Join the Creative Cloud and pay the monthly fee
- Join the Creative Cloud (Single App) to get Illustrator CS6 and pay the monthly fee