Index: t3lib/cache/backend/class.t3lib_cache_backend_filebackend.php
===================================================================
--- t3lib/cache/backend/class.t3lib_cache_backend_filebackend.php	(revision 7190)
+++ t3lib/cache/backend/class.t3lib_cache_backend_filebackend.php	(working copy)
@@ -93,9 +93,18 @@
 	public function setCacheDirectory($cacheDirectory) {
 		$documentRoot = PATH_site;
 
-			// resetting if an absolute path is given
-		if ($cacheDirectory{0} == '/') {
-			$documentRoot = '/';
+		if (TYPO3_OS === 'WIN') {
+				// convert backslashes on window machines
+			$cacheDirectory = str_replace('\\', '/', $cacheDirectory);
+				// look for absolute path
+			if (strpos($cacheDirectory, ':/') !== FALSE) { // Windows path
+				$documentRoot = '';
+			}
+		} else {
+				// resetting if an absolute path is given
+			if ($cacheDirectory{0} == '/') { // Linux path
+				$documentRoot = '/';
+			}
 		}
 
 		if ($cacheDirectory{strlen($cacheDirectory) - 1} !== '/') {
@@ -111,14 +120,14 @@
 
 		if (!is_dir($documentRoot . $cacheDirectory)) {
 			throw new t3lib_cache_Exception(
-				'The directory "' . $cacheDirectory . '" does not exist.',
+				'The directory "' . $documentRoot . $cacheDirectory . '" does not exist.',
 				1203965199
 			);
 		}
 
 		if (!is_writable($documentRoot . $cacheDirectory)) {
 			throw new t3lib_cache_Exception(
-				'The directory "' . $cacheDirectory . '" is not writable.',
+				'The directory "' . $documentRoot . $cacheDirectory . '" is not writable.',
 				1203965200
 			);
 		}