What exactly is Mahoutsukai Tai! to you ask? Mahou-tai is a 6 episode OAV (direct-to-video) anime series, a 13 episode TV series, 3 volumes of boy-targetted manga, 4 volumes of girl-targetted manga, and a series of Japanese books. That's a lot to keep track of, and kind of confusing ^_^; Let's start with the OAV series, because that's where the commercial release starts and what most sites on the web are more familiar with (including this one).
There are half a dozen translations of the title scampering around the internet. The title is a pun - the way it's written means both "Magic User's Club" and "I want to use magic" (and some others, so I hear); both are correct, but I like to translate it as the former. It is about a Magic Club afterall ^^ Yes, I love Media Blasters because they agreed with me ;)
The plot of the series is very simple. Aliens (the tsurinage or "the bell") come to earth, shoot down the UN forces, and... stay. They don't bother anybody, they just exist. However, a certain magic club take it upon themselves to discover the Tsurinage's motives, only to get caught up in more than they bargained for. The OAVs follow the day to day life of the club (focusing on the main character, Sae) as they fight aliens, rival clubs, practice magic, avoid the press, and get caught up in all sorts of love triangles. It's a great romantic comedy with a slight perverted twist ^^;
And from there, the various versions diverge. The manga series each emphasize different aspects of the plot, like the romantic angst - Tammy Ohta's shoujo version - or the perverted humor - Sham Neko's shonen version. For more information on either visit my MTT! manga page. The TV series picks up right after the OAVs left off, following life for the magic club after the Tsurinage/Bell (for a smidge more information visit my MTT! on TV page). I haven't a clue about the 4 novels, I haven't seen them and I'm not fluent in Japanese to try and read them ^^; My website primarily focuses on the OAV series - it's where I discovered MTT, afterall.
Supposing you're interested. How do you acquire this series? Media Blasters / AnimeWorks has commercially released the anime in North America under the title of "Magic User's Club (Maho Tsukai Tai!)". The first 3 VHS/DVD cover the OAV series and then VHS/DVDs volume 4+ span the TV series. The DVDs have Japanese and English language tracks and a few extras, the VHS as far as I know are dub only. For a random impression on the early volumes of the commercial release, visit this page.