When you get the next one please just make a note of it. I know it's a pain with all those zeros etc but it does mean something.
Managed to take a look at the minidumps. Most recent ones shown below with bugcheck string and code and which driver caused it.
05/08/2010 11:04:40 SYSTEM_SERVICE_EXCEPTION 0x0000003b win32k.sys
05/08/2010 10:20:42 SYSTEM_SERVICE_EXCEPTION 0x0000003b ntoskrnl.exe
05/08/2010 09:49:12 NTFS_FILE_SYSTEM 0x00000024 Ntfs.sys
14/07/2010 23:31:12 PAGE_FAULT_IN_NONPAGED_AREA 0x00000050 ntoskrnl.exe
14/07/2010 22:59:48 PAGE_FAULT_IN_NONPAGED_AREA 0x00000050 ntoskrnl.exe
14/07/2010 22:29:54 PAGE_FAULT_IN_NONPAGED_AREA 0x00000050 ntoskrnl.exe
14/07/2010 22:01:54 SYSTEM_SERVICE_EXCEPTION 0x0000003b win32k.sys