Anyone know where I can get a copy of IPB 1.3 (the last free version)?

You may not:
permit other individuals to use the Software except under the terms listed above
reverse engineer, disassemble, or create derivative works based on the Software for distribution or usage outside your web site
use the Software in such as way as to condone or encourage terrorism, promote or provide pirated Software, or any other form of illegal or damaging activity
modify and/or remove any copyright notices or labels on the Software on each page (unless copyright output removal license is purchased) and in the header of each script source file
distribute the Software
distribute individual copies of files, libraries, or other programming material in the Software package
distribute or modify proprietary graphics, HTML, or CSS packaged with the Software for use in Software applications other than Invision Power Board or web sites without written permission from IPS
modify the software to function in more than instance or location (URL, domain, subdomain, etc.) from a single set of source program files unless each location is separately licensed

http://invisionboard.com/?license