So, you're interested in Seven of Seven, AKA Shichinin no Nana, are you?
Well, it's "what happens when you let Yasuhiro Imagawa create a shoujo series"; the guy previously did G Gundam and Giant Robo.
It also involves what happens when you let Mine Yoshizaki do the character designs and influence the story: The Nanas look like one of Natsumi Hinata's classmates, and recurring guest characters are Melody Honey (one of the characters from Arcade Gamer Fubuki, and also a recurring guest character in Keroro Gunsou) and radio host "Examinee 623"/"Mutsumi" ("6 2 3 spells Mu Tsu Mi". Yeah, and it also spells Saburo, wave-buddy to Kululu).
Basically, a teenage girl (Nana) screws with an experiment, and gets 6 sisters/clones/whatever (for a grand total of 7 Nanas). Now, they have to get through the final year of junior high, pass high school entrance exams, try and get close to the guy they have a crush on, and moonlight as sentai heroes while keeping the increased number of Nanas and aforementioned moonlighting as sentai heroes secret.
Oh, and they have to all somehow recombine within a year, or they all disappear.
The show is notable for the voice actors used, both in Japanese and English versions: Nana Mizuki in one of her role prior to being cast as Fate, while in English, Veronica Taylor plays all seven Nanas, and manages to give them all different voices, while Rachael Lillis plays Nana's best friend, Hitomi. In both versions, Yuichi is Xellos.
So, enough intro, off we go!
EDIT: Okay, a couple notes I forgot to put in the initial version:
First off, I'm using the dub.
Second, there are 25 episodes, plus a bonus 26th episode that takes place between episodes 19 and 20 (I'll be keeping it as episode 26, since it has some spoilers if it's chronological order, but are not spoilers if you watch it last). In the series box set that I have, the first two discs have 5 episodes each, while the other four discs have 4 episodes each.
Oh, and the DVD menus give a different name to many of the episodes than the ones actually seen in the episodes. I'm using the names given in the episodes, not the menus.
Each episode is a TV show half-hour (which works out to actually be somewhere between 20 and 25 minutes, depending on the show), with one story per episode, and a running story throughout the series.
I only know of one spot where a commercial would go in each episodes, and that's mid-way through. Since it's likely I'll be putting up long posts, I'm cutting each episode in half at that point, and posting each part separately.
Also, I haven't watched the series in a few years, so I'm going through it as I do this.
Finally, here are the opening and... hmm, I can't actually find the ending credits...
Anyway, the intro theme is "Success, Success", sung by "nanaxnana" (AKA the Japanese V As of the Nanas), and the ending theme is "Birdie, birdie", sung by Nana Mizuki.