What Splunk enterprise version could I use to capture all the logs to include Windows XP, 7 and server 2008 and Solaris 9? Currently have Splunk 6.5.3.
From the Splunk page for Previous Releases :
If you require a version that is not listed please contact Splunk Support.
https://www.splunk.com/en_us/download/previous-releases/universalforwarder.html
You will need to contact Splunk Support to find a version that suits your use case.
I can't find a version that supports those antique operating systems so you're probably stuck with 6.5.3.
That version of the UF is only compatible with indexer versions 7.1-7.3. To run Splunk 8 on your indexers, you'll need to install intermediate heavy forwarders running version 7.1-7.3. See https://docs.splunk.com/Documentation/VersionCompatibility/current/Matrix/Compatibilitybetweenforwar...for the compatibility chart.