EXS 24 Logic Sampler Users Group

Hi everyone,
Desperately need help on this one: Trying to use a 17" titanium laptop for live 
music: MacOS X, Logic 6.1, Motu 828. The problem: when I have up to four 
songs opened (each one with five to eight EXS instruments )  everything is 
alright. As soon as I open the fifth song the exs instruments start to loose the 
samples they were previously absolutely fine in working with.
To make things more complicated I used to do the same  thing on my old G4 
laptop on OS 9 and Logic 5. So, apart from making OSX/Logic 6 versions of 
the songs everything remains the same. For example in OS 9 all the songs 
opened at the same time would not use more than 400mb of memory. Now in 
OSX I know that with 4 songs opened Logic is still using only 30% of the 
power available.
Anyone had this problem before? Sorry if it has already been discussed here, 
I couldn't find anything...
Thanks,
Mano