Feel free to use the generated audio for any of your projects (commercial or personal). It's free! Hope it's useful for you :)
This online tool lets you generate a Microsoft Samstyle voice (not the exact original) that you can play and download easily.
Just wait for it to load (it may take a minute or so as it's a 2mb piece of software) then type your text in the box and click "Speak". You can download the speech by clicking the link that will appear under the "Speak" button.
Old-school text to speech is great fun to play around with. Try testing it on long or hard to pronounce words, use it to narrate your silly YouTube video, post it as a message to a friend's facebook wall - the possibilities are endless.
If there's anything I can do to improve "Microsoft Sam Online", please let me know!