Setup:
1. Obtain a SM64 rom
2. Extend it with the SM64 rom extender here: http://homepage.mac.com/qubedstudios/Mario64Tools.htm
3. Drag you rom over rom_expand.exe
4. Patch "SM64 - Christmas Carnival Special.ppf" to it using "PPF-O-MATIC"
5. Play using an N64 emulator (with memory set to 8mb) have fun!

Hack by Skelux

If you are interested in making your own SM64 hack, here I
the tools I'm using.

Toad's Tool 64 (Placing obejcts, editing levels): http://homepage.mac.com/qubedstudios/ToadsTool64.htm
Mario 64 Level Importer (Importing custom models in): http://sites.google.com/site/messiaen64/level-importer
Music XML Alpha (Importing MIDI music in): Avaliable in downloads at bottom of level importer page
Mario 64 Text Wrangler (Editing text): http://homepage.mac.com/qubedstudios/Mario64Tools.htm
MadEdit (Hex editor for the more complicated stuff): http://madedit.sourceforge.net/wiki/index.php/Main_Page