According to the Hollywood Reporter (sorry, xtmont) blurb about the deal, the proposed TV series will be about a "25-year-old former slacker" who reluctantly adopts the Starman mantle after his brother, the former Starman, is mysteriously killed. That's pretty sketchy, but it seems to track well with the established comics continuity.
In the comics version, Jack Knight was the son of the original Starman, a Golden Age superhero. Jack never showed much interest in superheroics, preferring to focus his energy on his pop culture memorabilia collection. Jack's older brother David became the new Starman when the original retired, but shortly thereafter was murdered by the son of one of his father's old enemies. Jack took on the role to track down the killer, and to fulfill his father's desire to have the Starman legacy continued.
The comics also featured an interesting potential tie-in to Birds of Prey continuity. In the 1950, the original Starman had an affair with the original Black Canary, the mother of the heroine featured in the Birds of Prey comic. Since the BoP TV show takes place in the future, and the TV Dinah Lance is much younger than the comics version, it's unlikely that this plot thread will carry over to the Starman series -- unless it's Jack's brother who had the affair with TV Dinah's mother, who may or may not have fought crime as Black Canary.
I highly recommend the comics series, the first 53 issues of which have been collected into trade paperback form. The collected editions are:
- Starman: Sins of the Father
- Starman: Night and Day
- Starman: Infernal Devices
- Starman: Times Past
- Starman: A Wicked Inclination
- Starman: To Reach The Stars
- Starman: A Starry Knight
If ABC commits to the series, look for it as soon as Fall 2003.