In most cases, the computer manufacturer has already configured the system to use the maximum amount of graphics memory that is possible for your particular laptop model.
Sometimes you can change these values through BIOS level. We would recommend to check with your laptop and motherboard manufacturer (for the system with the Core i3-2120T) if there are tips on increasing the amount of graphics memory for your computer model.
If you are interested in additional information see graphics memory frequently asked questions:
Thanks for your response.
I have already looked into the BIOS (UEFI) settings for the HTPC, and DVMT is enabled and set to use at least 256MB RAM. Whilst the system reports this as the 'Minimum Graphics Memory', the 'Graphcis Memory in Use' sits below this most of the time (and occassionally below the important 64MB threshold that causes Media Center warning messages to appear).
The ASRock manuals and support (for the HTPC motherboard) are very good, but indicate that Windows 7 will ignore these once the system has started up.
The Dell laptop has its BIOS (UEFI) setting locked by Dell, but it too is specifying a DVMT RAM value (of 64MB in this case), but that system has also been observed to drop below this defined minimum.
These suggest to me that the Intel driver lacks a proper definition of the 'minimum' to the CPU...