Since you're looking for a DOS solution, last week's post was almost identical and the consensus was:
Command line tool to delete folder with a specified name recursively in Windows?
for /d /r . %d in (.svn) do @if exist
"%d" rd /s/q "%d"
or
for /f "usebackq" %d in ("dir .svn
/ad/b/s") do rd /s/q "%d"
Actually, SVN also gives you the option to export a working directory without the .svn/_svn directories.
Afterthoughts, three years later:
I think the reason people end up needing to recursively delete the .svn/_svn folders is because they've directly copied their local working copy to a new location in order to do a folder comparison of their modified version compared to a clean export, i.e. after something goes awry with the modified local working copy. (At least that's why I've needed it. It's definitely easier/faster to just use 'svn export' when that's possible.)
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