The screen stretching occurs as the BIOS screen is displayed and remains like that until kdm is loaded. The motherboard is of the same make as the laptop but a different model. All connectors fitted properly without necessitating the least of modifications.

Is it possible to correct this issue so that the screen is properly displayed without the stretching?

Laptop: Acer Aspire 7715z

Am I correct when stating that the graphical terminal is stretched and the GUI is OK?

You mention Debian in your profile, if that is the distro used have a look at the following file: /etc/default/grub

Especially this part:

The BIOS screen is appearing overstretched by a factor of 200%. This behaviour continues when GRUB-PC boots, when the kernel boots and when kdm loads. Since this appears as soon as the BIOS takes control, I am concluding it has to do with the hardware of the display, the is, the GPU (integrated with the chipset) and the laptop display.

I rechecked the order confirmation email and verified that the laptop model is the one that I have - this motherboard should be the correct one because everything fitted properly. The only problem is the overstretched display.

Does anyone know of a solution to try?

Maybe too obvious, but have you checked your BIOS settings? You do mention that the MB is same make, but a different model.

I was of that impression but I checked my emails and confirmed it must be the motherboard that I need. I am thinking it must be the BIOS.

When it powers on, it is set to 640x480. That's what the bios sets. Is that overstretched?
If not, does the stretch come in after grub loads, or the kernel?

The BIOS Setup Utility is stretched and the stretching persists even while kdm is running. I didn't load KDE because clearly the problem would also have persisted since kdm depends on X.

Because of this, I am trying to use the old motherboard which didn't exhibit this problem. I will attempt to override the problem by modifying the BIOS.

Fire away on the BIOS, but be sure to keep the old one, or get a copy.

I think the bios just sets a default mode - it shouldn't actually have to do that as a card should power up in a default mode of 640x480. It sounds like your default mode is 1024x or 1280x. It could be bios setting those modes. Here's the real test. Before you get into setup, it prints up some data about the box or video. Is that stretched?
Another possibility to consider is that there's a lot of eeprom in the chipsets configuring them. If the chipsets on the motherboard are [U]configured[U] differently, there's really nothing you can do about it.

10-12 years back, Via had this overly famous 'hardware fault' on large block copies in their PC chipsets. It was actually because manufacturers had tweaked the settings in the chips so the Creative Soundblaster would work. So we owners got utilities and suggestions to tweak them back for ourselves, on a purely "At Your Own Risk" basis from Via. I tried them, and they worked. But I didn't have to do much, because although I had an MPV3 southbridge, I didn't have the 'hardware fault'. It just cemented my opinion that VIA, and Creative, for that matter, were poor hardware.