Audacity! GarageBand! Those are two progams to make you sound like alvin and the chipmunks but there is way more! Don;t you find it dun to sound like Alving and the Chipmunks? Too bad I do... I personally think Audacity is the best program to use for this because (I'll get to that later) and I think Garage band isn't as good because it only gives u helium voice. In Audacity (back from up there), you can change pitch and move it up and down until you get it right. Also Audacity is a FREE program but Garageband? Thats Free too i think haha. But Audacity doesn't take up as much space. But this isn't what I'm talking about so back to the POINT! If you want to try sounding like Alvin And the Chipmunks, why not try Audacity? you can try sounding like other people too but you can find that out yourself, its really easy with some tools. What you do is you record/upload you sound and then select All (Ctrl+all) and then click change pitch in the Effects thing. Then you change the Pitch thing to: C to A#/Bb. Then click ok and listen! Also to export as mp3 you will need to have another small accesory: lame_enc.dll.
Here are some helpful links:
Audacity: http://audacity.sourceforge.net/download/
Alvin And chipmunks guide:
http://www.instructables.com/id/How-To-Chipmunk-Songs/#step1 (go through the steps by clicking on small pics, you will see)
MP3 Export file, lame_enc.dll: (copy and paste this link, it is download) http://lame.buanzo.com.ar/Lame_v3.98.3_for_Audacity_on_Windows.exe