Running 6.3 and 6.4, once I open in a separate window, it locks everything up. Would love to be able to use my other monitor, too. I wonder if this is the key. I retired from my coding days years ago and never did Java. I am willing to give this a try if someone can point me in the right direction. Thanks.

If giving "this" a try means you would like to try editing the startup parameters, the process is the similar to the one described for increasing the memory allocated to Java. This is documented in the FAQ, see: How can I adjust the memory used by Sweet Home 3D? in:
http://www.sweethome3d.com/faq.jsp

Instead of modifying the text described in the FAQ, use a text editor to insert the following:
Backup the existing file before changing it.

I can't be more specific because exactly what needs to be edited varies depending on your operating system. Note, you're not editing Java code, rather you're just altering scripts or config files (similar to mainframe JCL, UNIX shell scripts, or application property files).