richmondody: 2. SSD: I suggest you get one for your OS. It is a bit pricey, but it's worth it. My pc boots in less than seconds because of it. A lot of people seem to recommend the Samsung Evo Pro series.
AlKim: My PC boots very quickly because I've got an ASRock motherboard with InstantBoot software. I don't know how quickly it actually boots, but so quickly that it's up and running well before I've returned from the bathroom ten feet away with my toothbrush, or so fast that I don't mind getting up at night to check my email. I'm certain that it's nowhere near as fast as an SSD (and that OS-related tasks aren't performed as fast), but that's one way of saving considerable amounts of money.
Mind you, I have never had an SSD, so what the fuck do I know. I might well jump in the bandwagon and start banging on about them the moment I buy one myself.
If you use Windows 8 and the default fast boot (which is basically a partial hibernate mode), it will also load Windows 8 in mere seconds, also with old HDDs.
I am not always sure if the people who say their Windows boots up in a few seconds with SSD are mostly referring to Windows 8 fast boot feature, which explains also the fast boot.
I have disabled the fast boot in Win8, though. If I wanted to be able to boot my PC as fast as possible, I guess I would be mostly using the sleep mode.