Prestige Classes you can qualify for in 5 levels or less...

[Someone]

From the expanded psionics handbook, you can qualify for Elocater easily with Psychic warrior 1/Fighter 4 (or psion 1/Fighter 4, or Psiwarrior 4/Fighter 1. The fifth level must be always fighter, and level 1, 2 or 4th). You can qualify for Slayer at level 4, Metamind, Thrallherd, Warmind, Piroquineticist and Psion Uncarnate easily at 5th level.

Pretty much all the prestige classes except Cerebremancer.

 

[Aenghus]

[Complete Divine]
Church Inquisitor

[Complete Arcane]
Alienist

[Complete Warrior]
Warshaper

[Player's Guide to Faerun]
Incantatrix

Aenghus

 

[Patryn of Elvenshae]

Well, then that sounds like entry at 6th level. Max ranks at level 5 in a skill is 8. Have to already have those ranks before taking a level in the prestige class, therefore 6th level is the entry point.

The question was, "What Prestige Classes can you qualify for in 5 levels or less?"

You qualify for TAc at 5th-level.

 

[Liquidsabre]

Complete Adventurer: Bloodhound (can qualify for at 4th level)

 

[saucercrab]

[Complete Divine]
Church Inquisitor

[Complete Arcane]
Alienist

[Complete Warrior]
Warshaper

[Player's Guide to Faerun]
Incantatrix

Aenghus

Yeah, like Aenghus said.

AFAIK, the church inquisitor is the lowest. A straight cleric can get into it at his 4th character level (so a clr 3/ci x).