I recently read that there is another Buffy movie in the pipeline. Is this true and if so, does anyone know what it will be about?

There is the possibility of a movie featuring a version of the Buffy character, but it not 'proper' Buffy from the show. The people who want do it were involved with the 1st movie, so they have rights to the Buffy character, but nothing else involved in the show so the movie wouldn't include or mention any characters or events from the show. They're doing it without Joss's permission or input (Buffy's creator) and without any actors from the show.
It's not definite yet, and frankly most fans are really hoping it doesn't happen, since not only is it a movie without any of the good things about Buffy (none of the show's writers, characters, actors etc) the people making the movie are pretty bad film makers. As far as I know they've never made a movie that wasn't a stinking flop, they almost ruined Buffy the 1st time round, and they are being pretty open about the fact that they are doing this just to make money with no regard for the character or fans. Most of the fans have been so against it that it may not happen, it's been made clear practically nobody would be willing to go see it.
If it does get made it will have to be set in an alternate timeline it would not be a continuation of the show.
If you need more info there are a lot of links about it on this spot :)