Mi sa che fai prima ad usare un programma che faccia tutto questo in automatico... in più questi programmi (Window Washer, Evidence Eliminator, eccetera) non si limitano a cancellare i files ma li sovrascrivono, così la privacy è garantita...

Questi programmi cancellano:
Windows SWAP file
Windows Application logs
Windows Temporary Files
Windows Recycle Bin
Windows Registry Backups
Windows Clipboard Data
Start Menu Recent Documents history
Start Menu Run history
Start Menu Find Files History
Start Menu Find Computer History
Start Menu Order Data
Start Menu Click History
Microsoft Internet Explorer temporary typed URLs, index files, cache and history
Microsoft Internet Explorer AutoComplete memory of form posts and passwords
Microsoft Internet Explorer Cookies (Selective cookie keeping for versions 5 and above)
Microsoft Internet Explorer Internet components (Selective keeping of components)
Microsoft Internet Explorer Download Folder memory
Microsoft Internet Explorer Favorites List
Microsoft Outlook Express v5+ database of (Selective keeping of mail and news groups)
Windows Media Player History
Windows Media Player PlayLists in Media Library
America OnLine Instant Messenger contacts
Netscape Navigator temporary typed URLs, files, cache and history.
Netscape Navigator Cookies (Selective cookie keeping for versions 4 and above)
Netscape Mail v4+ sent and deleted e-mails
Netscape Mail hidden files
Customizable lists of files and folders, with or without their contents
Customizable scan lists of file types in specific folders
Customizable scan lists of file types on all drives
Deleted filenames, sizes and attributes from drive directory structures
Free cluster space ("Slack") from all file tips
Magnetic remenance from underneath existing files/folders
All free unallocated space on all hard drives
Slack space and deleted entries in the Windows registry
Created and modified dates and times on all files and folders
Windows Registry Streams
Common Dialog load/save location history
Instant secure deletes of Windows registry data (NT4/2000/XP)

inoltre sono presenti dei plug-in per tanti altri programmi (winzip, winrar, zonealarm, office, ecc. ecc. ecc.)

Fare tutto a mano in un file .bat la vedo un po' ardua...
...se sei interessato, ne puoi trovare altri qui.