I have successfully configured a Splunk Unversal Forwarder to read the local machine's eventlog.
However, Splunk doesn't appear to be able to read the "Data" information in Events. This is the section displayed as either a byte or word block the bottom of the Windows Event viewing dialog control.
The host server is quite old running Windows Server 2003 R2 Standard Edition Service Pack 2
Is it possible for Splunk to read this additional data?
I'm not sure why you're not seeing this, as this is normally in the output. As you know, for some types of events, much of the relevant information about the event is contained in there, and many of the Splunk applications make use of this to be able to properly report. (e.g., if you have a security audit event, the file name is in the data section).
Windows 2003 R2 should be new enough.
In some cases, if a DLL containing the data template is not available to Splunk, it may not be displayed. Could that be the problem, say, permissions for the Splunkd user to the DLLs that contain the event data text?