My wife is into vintage video games.
http://www.videogamesprites.net/
Her input on this:
As you know, there is an original Pac-Man that was released to arcades. Then the Pac-Man game was ported to various consoles, such as Atari 2600 and Nintendo Entertainment System. The general consensus among Pac-Man fans is that the ports are inferior to the arcade version. Die-hard Pac-Man fans have pointed out that some "patterns" that work on the arcade version don't work on the ports. (Patterns refer to the movement of the ghosts.)
You may be able to buy a copy for your PC, but I am not sure if those ports are true to the arcade version.
One of the best ways to play a true copy of Pac-Man, if you don't have access to an arcade machine, is to download the MAME emulator. (MAME stands for "Multiple Arcade Machine Emulator.") Unfortunately, this requires a little more technical know-how, but it's not hard.
The MAME web site:
http://mamedev.org/about.html
MAME tutorial:
http://www.fantasyanime.com/emuhelp/emuhelp_mame.htm
Once you have MAME on your computer, you can download the Pac-Man ROM. (ROM is the term used for the game; it's basically a dump of the original game cartridge.)
There are many sites where you can download MAME ROMs, but some sites are less reliable than others. Be careful of the sites that are loaded with pop-ups and requests for you to vote for the site. These sites are difficult to use and sometimes contain malware.
Here is a site that explains some sources of Pac-Man:
http://www.xensei.com/users/jeffm/www/pacman/pacman-where.html