-- if you want to only see the folders named _vti_cnf:
get-childitem -recurse -force -filter "_vti_cnf"
-- remove all folders named _vti_cnf with prompt:
Get-ChildItem $RootDir "_vti_cnf" -force -recurse | Remove-Item
-- remove all folders named _vti_cnf without prompt:
Get-ChildItem $RootDir "_vti_cnf" -force -recurse | Remove-Item -recurse
Get-ChildItem $RootDir ".svn" -force -recurse | Remove-Item -recurse