TripleA is a gimped up replacement for the Hasbro CDRoms of Axis and Allies. However, it does have support for every flavor of Axis and Allies now.
You should be aware that the Artificial Intelligence makes the strategy of my 5 year old seem the work of geniuses. Also, the game has a tendency to crash - a lot - if you are attempting to do just about ANYTHING else on your system at the same time. Meanwhile, if you have any firewalls between you and the internet, you can pretty much kiss off having the firewall protect you OR playing the game (your choice) with friends over the internet.
Now, that said, TripleA is an awesome platform to use if you want to play some ideas out against yourself to iron out some ideas.
If you want to play with other users, your best bet is to get ABattlemap and use a dice server like the one built in on this site or at frood.net or failing that, if you like pretty pictures and a slightly more cumbersome mapping utility (cumbersome because it sacrificed some of the features of battlemap to build other features in like arrows and text blocks so you can leave notes, etc) you can get Mapview.
All of them can be found at DAAK.de (if they are up again), Flames of Europe (FoE), AAMC or, if you shoot me an email I can see if I can zip them up and send them too you. Though, you can find almost all of them for free by punching them into google or another search engine.
(In case you didn’t notice, I am heavily biased against TripleA. I think it’s a cute program just like the Disney Car’s video game my 5 year old plays on, but I wouldn’t use it for anything serious. It’s just too much a security risk and it’s about as flaky as Windows 95b (the one with Active Desktop installed for the first time) was in how stable it is and how well it works with other programs.)