Update 03/09/2015:
Managing path-based authorization rules for Subversion repositories is now possible through PowerShell. Check VisualSVN Server | Scripting and Automation page.
VisualSVN Server 3.4 and newer provides PowerShell cmdlets for server and Subversion repositories administration. Therefore, to manage access rules and automate such kind of tasks, you can use the following cmdlets:
There are a lot of other PowerShell cmdlets introduced in VisualSVN Server 3.4. For the complete list of PowerShell cmdlets and usage examples, read
the article VisualSVN Server PowerShell Cmdlet Reference.
Check SVNBook and VisualSVN KB article for description of path-based authorization. This is not Windows Access Control, it's path-based authorization and you should understand the difference in order to configure and manage access rules correctly and effectively.
I'm confused by the question, in fact. VisualSVN Server has a nice GUI implemented as MMC snap-in, allows you to manage svn users / groups and access right via a familiar GUI. When you use Windows Authentication you manage users and groups via standard Windows / Active Directory tools.