Okay so I did this, this morning about 4 AM. Without rewatching the youtube video I simply went for it.
It was easy peasy. The only stumbling block that I had was figuring out where a couple of the screws were that were hiding from me (lol).
Turned out that 2 of them are in the RAM compartment, 2 of them are under the rear rubber foot pegs and 2 more are behind the screen under the plastic cover.
Anyway, once I got all the screws out and thus removed the rear plastic cover behind the screen (no the screen does not physically need to be removed to replace the HDD or the battery as it turns out), it then became really simple to split the case using an old credit card. Don't use a screwdriver to try to do it as you WILL mar the edges of where the case splits in half, the plastic is actually quite soft.
Anyway, it took me about 2 hours to split the case, put in the new HDD and put it back together, that was with being quite lazy, smoking a few cigarettes and having a couple cups of coffee.
I'm now in the process of making a bootable windows 8 flash drive using the Microsoft tool to make it easier. I wanted to put Win 7 on it but I'm pretty sure that Asus doesn't have all the necessary drivers and or software to use this laptop under Windows 7 unfortunately.
Anyway, it was rather simple straight forward process but if you do not feel comfortable doing it, then take it to a computer repair shop that is reputable in your area.
I will not hesitate to do it again when I can find an affordable, really large SSD to replace the 7200 RPM that I just installed in it.
I was actually a little disappointed that I was correct that the HDD that came with this G46 is a Seagate 5400 RPM 8MB cache 750 GB HDD.
One would think that Asus would have either put in an SSD or at the very least a 7200 RPM 16MB cache HDD for better performance in one of their "gaming laptops". Oh well, it's got one now.
I have to say though... I suspect that getting Windows 8 on the hard drive will be the hardest part of the whole procedure, as it is now it's not going well. Seems bios is now refusing to boot from the USB thumb drive s I'm formatting it to FAT 32 as suggested in another topic to see if that helps any.