Oh dear what a lot of misinformation! A quick read of JAR-FCL1 would answer most of the questions posed here.
To answer BirdSeeds original question:
A CPL is a basic level professional licence to permit remunerated flying including Instruction. The groundschool requirement is either a 200 hour Modular course, or a 300 hour Integrated course. (The 100 hour difference is a credit for having an ICAO PPL)
To add a IR to either a PPL or a CPL there is an additional 200 hour ground school course.
The ATPL groundschool course is 750 hours reduced to 650 for PPL holders. Considerably more and encompassing all of the above.
As RC said you cannot get an ATPL unless you have held a CPL/IR. The so called Frozen ATPL does not exist, there is nothing to be unfrozen, nothing will magically happen when you get 1500 hours, you will still have a CPL/IR. What it means is that you hold a CPL/IR with ATPL level knowledge. You will still have to apply for, and pay for the issue of an ATPL once you meet all of the issue requirements, including 500 hours of Multi-pilot operation.
The ATPL Skill Test is effectively the Type Rating Skill Test on a Multi-Pilot aeroplane.