Couple questions 1. do you have to have the SVNadmin.exe software if you don't want the plug-in create repositories?
2. I can't seem to get the setup for agent to recognize the local repositories, it keeps wanting to create a new one.
3. What is the syntax to set up tortiseMerge for the diff and merge functions
Initial installation with TortoiseSVN
No. The plug-in will work with any existing repository.1. do you have to have the SVNadmin.exe software if you don't want the plug-in create repositories?
But you do need to have the svn.exe client utility and generally SVNadmin.exe comes as part of this same installer.
So if you want to make sure the plug-in does not create a repository just make sure the SVNadmin.exe is deleted form the machine.
The only thing you have to insure is that the version of the svn.exe client is compatible with the version of your repositories.
The plug-in should work fine with any version of the svn.exe client.
Consider this image:2. I can't seem to get the setup for agent to recognize the local repositories, it keeps wanting to create a new one.

The folder entry field and the protocol drop down define the location of the repository.
So for your case the protocol will be File and the Folder entry field should be the local folder that holds the repository.
Now if this is what you have done for your setup then I suspect the problem might be the version of the svn.exe client is newer the version of the repository maybe

You should be able to find this out by turning on the help debug option (see image above) and then looking at the log file.
Feel free to send me the log file as an e-mail attachment (e-mail button below) if you can get this working.
The external difference tool is setup using the command line entry field (see image above).3. What is the syntax to set up tortiseMerge for the diff and merge functions
The plug-in will provide two file names $f1, $f2 and two version $v1, $v2 numbers and you use these values to define the command line.
Some examples of typical command lines are:
Cheers Jussihttp://winmerge.org/
"C:\Program Files\WinMerge\WinMergeU.exe" /dl $v1 /dr $v2 "$f1" "$f2"
http://www.sourcegear.com/diffmerge/
"C:\Program Files\SourceGear\DiffMerge\DiffMerge.exe" "$f1" "$f2"
http://www.grigsoft.com/download-windiff.htm
"WinDiff.exe" "$f1" "$f2"