Potted history.... First heard the ACARS data bursts years ago and wondered what they were. Forwarded example to a mate who wrote me a program to decode the contents. The program developed into a product called Airmaster which was marketed by Lowe (and an early version was branded for AEA/Timewave in the USA). Making sense of what was seen on the screen was great fun as there was no real info available to the public. Ed Flynn in the USA was the only other person I knew to be interested at the time. He went on to write a book called "Understanding ACARS" which was published by Universal Radio Inc.
Ed and I e-mailed each other regularly and slowly found other people who were interested (my interest was the radio not spotting). Small group grew a bit and I set up a mailing list and the first ACARS hobby website with decoded examples, details of different airlines use of ACARS, logs from software etc. Soon after this I had my first nasty letters from airlines (they gave up eventually). Bart Hoekstra came along with a nice piece of database software to extract info from the software logs and the spotters started coming on board in droves as they could mark off frames even if they'd not read them (I've never understood spotters like that). Eventually I exhausted the technical interest side and moved on to other things. Nick Birrell, Tony Orr and others carried on with what I'd started. Eventually they merged our info with the commercail software site of Mark Avery as the site you quoted. Mark isn't making enough money selling his software so the site has largely dried up.
In the interim lots of other software decoders have been released with loads of spotter-friendly features.
ACARSD is pretty nice and excellent value for money - share ACARS data all over the world (so i guess the oddball spotters can now just mark off any frame fitted with an ACARS unit!). Multi-platform support and it's free.
Thanks for your interesting reply, I am looking into what is needed and how much it will cost to start receiving ACARS.
Radio, with headphone socket, capable of receiving VHF Airband Cable to take audio from radio to PC PC, with soundcard, running any operating system Software (from free to very expensive depending how much you want to spend)
I have all the above all I need is to try a free version of the software first.
ACARSD is free and has a good set of features. Using it you can even do away with the radio and cable if you don't want to tie up a radio. I'm not sure how good coverage of your immediate area will be as I've not looked at the list of servers for a while. You can share your own data with other users so if you are in a nice high spot with good VHF coverage you could make your data available to all the other list members.
For completeness I'd better add that very few military aircraft use ACARS