The original 5-key beatmania series has long ended, including beatmaniaIII, hence versions of both known by "The Final". 7-key beatmaniaII [DX], however, is still amazingly popular and makes tons of money for Konami. 14th Style ("GOLD") is scheduled to be released in the USA soon; it will be the first official IIDX arcade release in the USA. GOLD was also tested in Europe, but evidently interest was not high enough for it to be offered. The USA did see a brief presence of original beatmania under the name "Hip Hop Mania". It flopped. IIDX runs on completely different hardware from original beatmania (1st-8th style run on "Twinkle", which is basically a Playstation with add-ons for video merging from a DVD player and extra sound hardware), and newer styles run off a PC running an embedded flavor of Windows.
pop'n music is also still well and alive in Japan. Everything after 6 runs on new hardware (6-8 run on, IIRC, Firebeat, and 9th+ run on Viper). 6 and older run on the same hardware as beatmania: "DJ Main", which basically amounts to a GX with a hard drive attached. To my knowledge, Firebeat and Viper have no emulators available. There was a test version of pop'n music (1) in the USA, but I'm unaware of any production for the USA or Europe regions.
If you want to play either game, you can buy the console versions, which are pretty arcade faithful ports. pop'n 8 and newer are very well done and available for PS2 (Japan region only). IIDX was released on the PS2 only, and home releases began with 3rd style, which was based on the 4th style AC engine. 6th Style and newer are pretty arcade faithful. I'd highly recommend IIDX RED and pop'n 12 to get started.
(Yes, I know way too much about Bemani arcades...)