A base install of Windows 7 32bit is roughly 16GBs and 64bit is 20GB. Winsxs contains drivers, fusion and side by side assemblies and should not be messed with. Your Patch Cache is unusually large and can probably be cleaned up. Just be careful what you delete. MSP files are Microsoft Patches and you should be able to delete them.
You may also want to enable view hidden system files and see if you have a hibernation file. This will eat up as much space as you have RAM. The quick way to disable hibernation mode and remove this file is.