As of version 1.4.0 and later, the TortoiseSVN installer doesn't provide the user with the option to set the SVN_ASP_DOT_NET_HACK environment variable anymore, since that caused many problems and confusion for users who always install everything no matter whether they know what it is for.

But the feature is still available in TortoiseSVN and other svn clients. To enable it you have to set the Windows environment variable named ASPDOTNETHACK to 1. Actually, the value of that environment variable doesn't matter: if the variable exists the feature is active.