Analtomy: Ravenloft is a part of Planescape but it has it's own exclusive setting as well.
1) Ravenloft was from before Planescape, as both the stand alone Count Strahd adventures, and as a campaign setting.
2) EVERY D&D setting from the 2nd edition era is technically part of Planescape. Just like every setting was technically part of Spelljammer too.
Stig79: As the title says. Al Qadim is part of the Forgotten Realms setting. It takes place in Zakhara, which is to the south\south east on the Forgotten Realms map.
DCT: Yes the setting is in FR but it was always branded as it's own setting.
Exactly this. The Al-Qadim boxed set did not have the Forgotten Realms logo on it. The three other separate FR settings (Maztica, The Horde, and Kara-Tur/Oriental Adventures) DID get the logo, because they were supposed to be played as part of FR, while Al-Qadim was supposed to be either separate, or, if you had the FR boxed set, you could use it as part of the campaign setting.
So yeah, Al-Qadim should be treated as a separate setting.