Fixing Screen Freezes - Almost There

For the past few months my enjoyment of this hobby has deteriorated due to the regular screen freezes that my system has been experiencing. I have honed down the screen freezes (not CTDs BTW), to simply how many clouds I have, and the cloud density chosen. When I set it to "High", the system rolls over and dies. When I set it to "Low" or "Fair Weather", it works.All other reasons suggested on these forums (seasonal/cpu heat/drivers/sound hardware acceleration/enabling of render to texture etc. etc. etc) have been looked at an investigated, to no avail.So - the good news is no more freezes. The bad news is I can only fly in nice weather. How do I crack this last bit? Is it memory? I only have 512 Mb RAM, but don't want to buy more unless I'm sure.Any thoughts?ThanksRichardSystem:* AMD 2400 thoroughbred* Coolermaster Jet 7 Heatsink (this is one mother of a heatsink and fan - keeps the CPU to below 50 degrees C during FS).* Radeon 9500 not overclocked.* 512 Mb RAM* XP SP2* FS9 patchAs an aside, the freezes are infuriating 'cos when it works, my setup is absolutely fantastic. I have UK VFR Terrain / Photoreal scenery / British Airports, and I've figured out how to attach it to my Garmin Pilot 3, so I have a real live GPS to work with. So at last - real VFR simming!