EXS 24 Logic Sampler Users Group

I am having a desperate time running Yamaha C7 (beatuiful piano 
samples)for EXS24.
I run Win XP on a 1.7ghz pentium 4 processor.
Software: Logic Platinum 5
Initailly I had 256mg RAM

After taking about 20min to load into the sampler, when I pressed 
keys, the samples would play with pops, clicks and other digital 
noise.
I have tweaked the performance of the pc for high-end audio, but to 
no avail.
Time and Space (who sold me the CD) suggested I upgrade my RAM to 
512mg. So I did this (this cost £150) and now am running with a 
whopping 768mg RAM.

The samples load in faster, but when played, I still get digital 
noise, pops and clicks, so it makes them unplayable.

I called the support line again, and now he suggested (again) 
upgrading the RAM to one GIG. This shouldn't be necessary! If this is 
the case, there was nothing in the spec of this CD that said I needed 
ONE GIG RAM! 
I could very well buy this, but I'm afraid the problem will not be 
sorted.

Have you ever experienced this problem? Is there anyway I can tweak 
the PC or Logic so that the samples play clean?

I am exteremely grateful for your help!!
Many thanks


DigiFran