Emulation is the process of running programs written for one piece of hardware on a completely different system. For example, a Mac emulator will allow you to run Mac programs in Windows.
(I'll be adding a lot more to this page over time - simple instructions on how to set up a variety of emulators.)
I use emulators to run old ZX Spectrum, Atari ST and arcade games - old stuff from the 80's which would otherwise be dead and buried. I do have a large collection of old Sinclair hardware including a ZX80, half a dozen ZX81s, 4 Sinclair Spectrums (16k and 48k), a Spectrum 2 128k and a Spectrum 3 128k. That, plus addons like ZX microdrives, ZX and Alpacom printers, boxes and boxes of original tapes, disks, microdrives and more. However, setting up one of those beasties just to bash around in The Hobbit for ten minutes is out of the question, and that's where emulation comes in.
Let's start with the ZX Spectrum. First, download ZX32 from the ZX Spectrum Emulator Home. It's only 1.4 megs - once downloaded, scan it for viruses then run to install. There are newer and better emulators, but this one is quick and easy to set up. (Actually, you can get Beta 2 of this emulator here. Unpack over the installed version to update.)
Now that you've set up an emulator, it's time to get hold of a couple of games. Some companies forbid distribution of their old titles (e.g. Ultimate and Codemasters) while others have gone out of business, couldn't care less, or have given permission. The World of Spectrum website is careful to obey the wishes of these publishers, which means that you're free to download any games from their site which take your fancy.
Let's start with Valkyrie 17 by the Ramjam Corporation. Click the link and you'll see the comprehensive entry in the Sinclair Infoseek database, including screenshots, cassette inlay and the game itself. You can download the game using the 'Perfect TZX tape image' link. Save this file to logical place - e.g. make a folder C:\My Documents\Sinclair and store the zip file in there. Once saved, open the zip file and extract the TZX - this is the actual game file, stored as a perfect duplicate of the original tape.
Now, ZX32 needs a bit of setting up. When you first run it you might see a message about unsupported colour modes. Tick 'Do not show this again' and close the warning. Next, click the Options menu and select Options from the dropdown. Click the Hardware tab and change the Default Model to ZX Spectrum 48K. Drag the Tape slider to 'Load the tape as fast as possible'. Click the Display tab and change the option to 512 x 384 Double Size. Now click OK to save these options.
Now click the ZX menu entry followed by Open. Navigate to wherever you extracted the Valkyrie 17 TZX file and select it. The 'Browse Tape Image' form will pop up, allowing you to select the segment of tape you wish to load. Choose the very first item in the list and click OK. If the emulator is paused, click the play icon in the toolbar to run it. (By default, ZX32 pauses whenever you switch focus to another program.)
Valkyrie17 is now loaded. Press ENTER to get rid of the title screen, then enter NO when asked if this is a pirate copy. On the next screen you can start the adventure. Use abbreviated English to order the game around - e.g. Look, Talk to girl and so on. Good luck ;-) When you've beaten this one, go back to World of Spectrum and download some more of the 15,000+ titles available. I recommend Lords of Midnight.