Intermittent BSOD ntoskrnl.exe (nt+7cc40)

I had another BSOD and gave up with my ATI graphics card and bought an Nvidia one. A week later - still no BSODs so it looks like the ATI card/driver was the problem.

Spoke too soon. Just had another BSOD - as on some other occasions when leaving Chrome. WhoCrashed says:

On Wed 02/11/2011 23:52:04 GMT your computer crashed
crash dump file: C:\Windows\Minidump\110211-16473-01.dmp
uptime: 00:47:54
This was probably caused by the following module: ntoskrnl.exe (nt+0x7CC40)
Bugcheck code: 0x1A (0x41790, 0xFFFFFA8006CC0A20, 0xFFFF, 0x0)
Error: MEMORY_MANAGEMENT
file path: C:\Windows\system32\ntoskrnl.exe
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: NT Kernel & System
Bug check description: This indicates that a severe memory management error occurred.
This might be a case of memory corruption. More often memory corruption happens because of software errors in buggy drivers, not because of faulty RAM modules.
The crash took place in the Windows kernel. Possibly this problem is caused by another driver which cannot be identified at this time.


On Wed 02/11/2011 23:52:04 GMT your computer crashed
crash dump file: C:\Windows\memory.dmp
uptime: 00:47:54
This was probably caused by the following module: win32k.sys (win32k!memcmp+0xF0D)
Bugcheck code: 0x1A (0x41790, 0xFFFFFA8006CC0A20, 0xFFFF, 0x0)
Error: MEMORY_MANAGEMENT
file path: C:\Windows\system32\win32k.sys
product: Microsoft® Windows® Operating System
company: Microsoft Corporation
description: Multi-User Win32 Driver
Bug check description: This indicates that a severe memory management error occurred.
This might be a case of memory corruption. More often memory corruption happens because of software errors in buggy drivers, not because of faulty RAM modules.
The crash took place in a standard Microsoft module. Your system configuration may be incorrect. Possibly this problem is caused by another driver on your system which cannot be identified at this time.

Seems to have been a double BSOD. As before am running out of ideas - very grateful for any of yours.

Thanks.

Here are the minidump files.