The Negima Intro OVA's were a series of 3 short episodes bundled with drama and concerts CD's before the airing of Xebec's adaptation on TV. These episodes are under 10 minutes each. The episodes introduce the audience to the classmates and loosely cover a few chapters of the manga. These chapters would later be cover more thoroughly in the TV adaptation.
The episodes spend a short time on the chapters before going and introducing the characters separately. Their intro's feature animation of later chapters, but does not cover the material.
Episode 1 briefly goes over Negi learning of his teaching assignment, cover Chapter 1
Episode 2 covers the love potion incident of Chapter 2
Episode 3 spends time covering Chapter 13 when the Narutaki twins take Negi around the campus and shows him the various activities of his students
It's also interesting to note that many of the character's designs and settings were changed between the release of these OVA's and the TV series to air a short time later.
Negima! By Studio Xebec
This was the first anime that aired on Japanese television for the series and is considered the closest adaptation to the manga. The series is 26 episodes and roughly covers the first 6 volumes of the manga. Many stories of early chapters are animated, including Negi's arrival, the love potion, etc. There are a number of differences between these episodes and the chapters, however. This anime mainly focuses on the slice-of-life elements from the early chapters.
The Kyoto arc is covered in two episodes, so a number of key plot points were removed, such as Setsuna's reveal as a hanyo, Cinema Town, and Kotarou Inugami was removed entirely. Sayo was also revealed far earlier on in the anime with an entirely new story altogether and was able to attend the Kyoto trip.
This series also includes an entirely original ending, making Asuna's origins completely different from its manga counterpart.
This series never received a direct sequel and another Negima anime series would later be taken up by Studio Shaft, but that anime would cover the spin-off series, Negima Neo.
Negima!? Spring Special OVA By Studio Shaft
This OVA is part of Shaft's Negima!? series, an anime that is based off Negima Neo's manga rather than the main one, but this particular OVA is loosely based on chapters 60-62.
The content of the episode is quite a bit different, featuring a different set-up to Asuna's behavior toward Negi, different activities among the classmates, etc., but the base of the story is still the same.
Many different bits were removed, such as Konoka asking about ways to form probationary contracts, Yue and Nodoka asking for personal magic training, and many other small details. Both are filled with plenty of hi-jinks, but this episode does have many quirks that would be present in the Negima!? series.
Negima! Ala Alba
Negima! Another World by Studio Shaft & Pastoral
This OAD series was released alongside the manga and covers certain parts of the story where Negi's team travels to the Magic World. The episodes do not quite line up for a narrative story, rather, they only pick and choose certain chapters to animate. Many of the chapters are condensed a bit to fit in the episode's length. Five episodes were made in for this series.
Episode one covers chapters 184-188
Episode two covers chapters 189-192
Episode three covers chapters 193-204
Episode four covers chapters 205-209
Episode five exclusively features the Yue-exclusive scenes from chapters 203, 210-213