It is quite dangerous to go in the Windows folder and start deleting things. Of course you don't need most of them, but Gates has decided that Windows needs them, so your opinion does not matter. Remove the files, and either Windows will break, or the Recovery machine will kick in and force you to replace them.
The best way to try and diminish the number of useless files is to use the Add/Remove programs in the Control Panel. Also, search the Web for pages on how to remove Netmeeting, and you'll get a few tips on removing Outlook Express and a few other things you might not need but cannot uninstall by default.
Also, get a good defragger, like O&O Defrag. Defragging will not make your files smaller, but it can recover space lost due to unnecessary clusters being occupied. The default Windows defrag is still unable to correctly defrag a disk.
Pascal.