Out Of Memory Error on high end system..Pls Help!!

I have recently upgraded my computer and am running FS9 on Intel Core Duo 6600 with 2GB 800mhz Corsair Ram + 7800GTX Asus card. Now whenever I fly PMDG's wonderful 747 400 PAX or CARGO after about 20 mins or whenever I am on a final approach to an airport I get an out of memory error and then the flight is over. I have searched the forums and have changed my page file so that it is 'system set' and I have 10100MB on 3 drives in use. Now If I start Task Manager and watch on the performance page and load the aircraft the page file goes from 345mb to 1.3GB and holds there.... the available ram drops to about 300000mhz so 0.3GB left. In cruise it pretty much stays around this point its not leaking any further the page file sometimes creeps upto 1.5GB and then when I get close to my airport destination bam I get the OOM error.... the question is if I add another 2GB Ram will this decrease the page file or is this a FS9 inherent problem its really annoying!!! Anyway any suggestions most welcome... I love my PMDG 747 and unfortunately I do not get this with other add on planes.... I am beginning to wonder if it could be a scenery issue although I have checked my texture folders etc...