Intuit,
Cey is referring to the SLIC table ("System Licensed Internal Code") in the BIOS that enables OEM Windows installs to activate via SLP ("System Locked Pre-installation"). With an OEM Windows product key that matches the SLIC table in the OEM BIOS, Windows would self-activate without going through Microsoft.
SLIC/SLP (ver. 1.0) was introduced with Windows XP, though if you could reflash a ver. 2.0 or 2.1 SLIC table in your BIOS you could install self-activated OEM versions of Vista or Win 7, respectively. (SLIC tables were backward compatible, so a 2.1 SLIC would self-activate all three OSes.)
Cey,
I don't think your BIOS is the problem, so you're barking up the wrong tree. A BIOS starts up in 16-bit Real Mode, and is never going to recognize more than 2TB drives. That's a function of Real Mode and the size of the sector registers in the MBR. Rewriting the BIOS can't change that.
When Windows boots, the startup files* kick the CPU out of Real Mode and into Protected Mode, where the operating system can then have access to 32-bit or 64-bit functions. Once in Protected Mode, the BIOS is out of the loop, and the OS can access disk drives of more than 2TB even if the BIOS could not.
Note that to install a 64-bit OS requires a 64-bit CPU. If your laptop is really old, it's CPU may only support 16/32-bit OSes. (If you had to modify the SLIC table, there's a very good chance your CPU is not 64-bit capable.) Note Steve's freeware "Securable" utility will quickly reveal if your CPU is 64-bit capable. If it's not, you're never going to get a 64-bit OS installed on that laptop, no matter what you do to the BIOS.
If your CPU is 64-bit capable, then you can install a 64-bit OS, and the BIOS doesn't matter. Remember, once it kicks into Protected Mode the OS controls disk access, not the BIOS, so a 64-bit OS can recognize GPT-style disks, including disks larger than 2TB, even though the BIOS doesn't.
However, the catch is the GPT disk has to be a secondary disk. You have to boot from a MBR disk but can use GPT for secondary disks. You can't boot from a GPT disk because the first part of the boot process relies on Real Mode and MBR, and that doesn't know what to do with a GPT disk so it would never get to the Windows startup partition to begin with.
To boot from a GPT disk requires UEFI firmware or a UEFI-capable BIOS. But that's a lot more involved than just reflashing your laptop's old BIOS, so isn't an option.
* (For clarity, I'm going to avoid calling them "boot files" because Microsoft perversely reversed the definitions so that, according to MS, the computer boots from the "System" partition and loads the operating system from the "Boot" partition)