Lots Of Crackles When Recording In Powerbook Options

[camarao]

Hi

I have a Powerbook 15" 1.67hz 512 mb ram and a 80gb 5400rpm hard drive and a Terratec Phase 24 firewire soundcard.
I have installed all my software ( Logic Pro 7.01 and Kontakt 2.01 ) and started to do some recordings.
I was using a loop in track 1 , a EVP 88 with a tape delay and nothing else. I recorded thru the digital ins a 24 bit stereo file coming from a 01V Yamaha digital mixer.
When I started to listen to the audio files ( 15 to 20 minutes )they were good in some places and terribly bad in others with lots of crackles.
Does the OSX run some kind of background application that was interfering with the recording process ? Are there any tips to fine tune OSX in a Powerbook for audio production ?
Are my Powerbook specs enough for this job or do I have to buy an external disk just to record a simple 24 bit stereo file ?

Thank you

Alex