Assuming you don't have an EFI firmware, I see a number of options:
- Ditch the computer and buy another one.
- Return your new disk (or use it somewhere else) and buy a 2TB model instead.
- If the computer supports two disks, use a sub-2TB disk for the Windows boot disk and use the 3TB disk (with GPT) for data. Note that you can probably get a kit to put a disk in your DVD slot. Since DVDs are much less important today than they used to be, this might be a good excuse to get yourself a small SSD for use as a boot disk. (Note that a BIOS-booted Windows 7 can use GPT as a data disk; the BIOS/MBR and EFI/GPT linkage applies only to the boot disk.)
- Resign yourself to using only 2TiB (about 2.2TB) of your new disk.
The above options are the ones that are the easiest and the least likely to cause problems. There are, though, at least two other options:
- You can, as you suggested, partition the disk in chunks. Because of the way MBR works, it's technically valid to create a partition that begins just below sector 2^32 (2TiB) and that has a size of up to 2TiB. I don't know offhand if the Windows partitioning tool will create such a partition, but it can be done. IIRC, I used Linux's
fdisk to do it. In my tests, Windows 7 was able to handle such a disk; however, my testing was extremely limited. There might be some serious "gotcha" that will end up chewing up your data. This is particularly likely if you've got 32-bit drivers that aren't explicitly coded to handle 64-bit disk addresses.
- You can try using DUET or Clover. These are both, essentially, software EFIs. They run as boot loaders on a BIOS-based computer, thus enabling Windows to boot from a 3TB (or larger) disk. One caveat is that they work best on Intel CPUs -- but I see your ASUS N61VN has an Intel CPU, so that's probably not a big deal for you. Clover is the prettier system, but it's a Hackintosh boot loader that will be easiest to set up if you've got a Mac. (Once set up, you can use it just for Windows.) DUET is less pretty by itself, but if you're single-booting you probably don't need the pretty boot menu; and if you did you could add rEFInd.
If you've got ~US$100 to spare and don't need a DVD drive, I'd probably go with converting your DVD slot to hold an SSD. I've seen conversion kits online for ~$25, and SSDs can be had for well under $75. The DUET/Clover approach can be quite effective, but it requires more in the way of technical skill, or at least the ability to follow technical directions.
This page provides instructions for a hack to enable installing Windows to a GPT disk to boot under BIOS mode. I haven't attempted to do this, but for somebody who still need to do this, it might be worth trying.