I have to agree with Rowport.
p.72 of Complete Arcane has several paragraphs which split hairs about how the Warlock can qualify for feats and classes that require "caster level X" (Caster Level), but not for ones which require "able to cast X level spells" (Spellcasting Level).
The only requirement for Practiced Spellcaster is 4 skill ranks in Spellcraft. Ergo, the Warlock can qualify for it at 1st level (Spellcraft is a class skill).
Now, as to whether he can benefit from it, it sounds like it. Practiced Spellcaster increaes your caster level. Warlocks have a caster level, and gain increased caster level from Prestige Classes that give "+1 level of spellcasting class" (this is mentioned specifically,
p.72 of Complete Arcane has several paragraphs which split hairs about how the Warlock can qualify for feats and classes that require "caster level X" (Caster Level), but not for ones which require "able to cast X level spells" (Spellcasting Level).
The only requirement for Practiced Spellcaster is 4 skill ranks in Spellcraft. Ergo, the Warlock can qualify for it at 1st level (Spellcraft is a class skill).
Now, as to whether he can benefit from it, it sounds like it. Practiced Spellcaster increaes your caster level. Warlocks have a caster level, and gain increased caster level from Prestige Classes that give "+1 level of spellcasting class" (this is mentioned specifically,