These are the best Sega Mega Drive (and other consoles) emulators available. Each one is slightly different in what they offer but they will all get you playing your favourite classic games well.
The best way I have found to play these is with a 6 button pad specifically the Microsoft Sidewinder Gamepads as its layout is similar to the buttons used by the console. The Gamepad exists in both 15-Pin analogue and USB versions and the Gamepad Pro is USB only. You can buy these from places like Amazon but Ebay maybe an excellent place.
To download the emulators, right click the links and select Save Target As... to save the file to your hard drive. All files are zipped so you will need to extract them.
Be sure to have the latest version of DirectX (9.0c) installed on your system. You can get it from here http://www.microsoft.com/directx
Requires Windows (Not NT) and DirectX 7
Fusion is a Mega Drive/Mega CD/32X, Master System and Game Gear emulator for Windows written by the god of Sega Programming Steve Snake.
It sports high accuracy, high speed and plenty of other options like Pro Action Replay support.
For full speed on all emulation modes you will want a processor running at 800Mhz.
Fusion is excellent since it does not require the dreaded ASPI layer. However, Kega does
not have a screen shot facility but Im sure it will eventually have. I have used previous
version of the emu for many years on numerous versions of Windows with no problems.
Download Kega Fusion
Requires Windows (Not NT), DirectX 7 and ASPI
Gens is a Mega Drive/Mega CD and 32X emulator for Windows Written by Stephane Dallongeville. It sports loads of useful features in addition to the emulation like debugging and screenshot grab used for much of this website.
For full speed on all emulation modes you will want a processor running at least 800Mhz.
To play all emulation modes at full speed a processor running at 1GHz will be enough. More info is in the emus read me file.
For playing Mega CD games this emulator requires the ASPI layer. See below.
Requires Windows (Not NT) and Direct X 7
This emu is based on Gens. This is very similar to Gens and has a few tweaks such as
turbo games and macros for quick button combinations. It can be set to appear in a simple
mode or an advanced user mode. Useful for those not familiar with emulation.
This is one of the first Mega Drive / Genesis emulators. It runs in DOS and is bested used with a Vesa display driver.
This has now been outdated by the Windows versions but if you still have a PC of around 166Mhz and Windows 95/98 then this would get you full speed emulation.
Simply unzip the file to a directory and run kgen.exe
These files are needed for optimum usage of these emulators (except KGEN). You will
have to configure each emu to look for these files. This is usually a case as point the emu
to the file location.
Download BIOS Files
This is a small driver that allows programs to access functions of CD ROM drives under Windows. This is mostly applicable to versions of Windows previous to XP however an APSI layer can be installed with no problems.
In the case of these emulators, the ability to load Sega CD and play their music.
Adaptec provide a download package. You can get it from http://www.adaptec.com and searching the support section for Windows ASPI Package. (v 4.71.2)
There does exist emulators for Apple Mac and Linux however these are not as advanced as their Windows counterparts. You will probably be able to get full Mega Drive/Genesis but not the other systems like Mega CD and 32X.