N64 emulation is a particularly odd duck. The creator of the only emulator that is still being actively developed asks users for a $20 donation in return for their downloading any release newer than 2005; and many games played on it still don't look or sound anything like the real thing. Nevertheless, the N64 emulation process is actually much more straightforward than jerry-building a PlayStation or Saturn emulator--and it offers a few unique tricks of its own.
First, about that $20 donation: The developers of the preeminent N64 emulator, Project64, certainly deserve the money; but you can get by quite nicely with the last public release (v1.6). Unlike with other modern consoles, you don't have to track down a BIOS image, and the default video plug-in--which, somewhat adorably, boasts full DirectX8 compatibility--will be more than sufficient for 90 percent of users.
Unlike many other emulators, Project64 has its own installer; but in other respects, the operational process is business as usual. Once you've installed the program, go to File, Choose ROM Directory to point it toward your games, and then tap F5 to refresh the main menu if you don't see the games in the list. Then double-click to start.
If you delve into the 'advanced settings' menu of Project64's video options, you should see an item labeled along the lines of 'override aspect'. Check the box next to this option, and if you're playing in any aspect ratio other than 4:3, the emulator will render the game in that aspect ratio without doing any stretching or cropping--and as a result, it will display more of the image than you ever saw on the original console (or for that matter, on the Wii's no-frills Virtual Console emulator).
This enlarged field of view is what I consider a magic emulation moment: No commercial publisher has ever offered any comparable enhancement, as far as I know, and yet this six-year-old emulator does it without batting an eye. The implementation isn't perfect--in some games, you can see the world geometry constantly being drawn and erased at the corners of your newly widened screen--but I'm willing to bet that if you've read this far, you probably find the program's rough-around-the-edges emulation more charming than disappointing.
Fans of Treasure's underloved Sin and Punishment, which recently received an excellent (and underrated) bona fide sequel on the Wii, may be interested to know that the entire game has been overhauled with fan-made, high-resolution textures, available from Vanit along with a tutorial and a special-purpose video plug-in for installing them. I'm not aware of any other games that have received this superneat treatment.