Steam

[Polemists]

Okay first, and less important,

Has steam ever been used before with a games for windows game? Sometimes things don't mix well and sadly I do have vista.


Secondly and more important,

If I had a file

let's call it demo

how quickly can steam download it? :P

[Husar]

Okay first, and less important,

Has steam ever been used before with a games for windows game? Sometimes things don't mix well and sadly I do have vista.

Now you're trying really hard to find something you cannot like about Steam, aren't you?
To answer this, afaik games for windows is just some "Microsoft approved" kind of seal that says the game should run on Microsoft systems and isn't the buggiest piece of software ever released, or maybe MS just takes the money and then gives the seal.
Either way it should not interfere with Steam.
I do have vista as well and the only big difference I noticed is that it takes a while to load while it's almost instantly in XP. Once it is loaded however, I haven't found any problems except that you can buy games that do not run in Vista, but then you could buy them on a CD and they would still not run in Vista.

Secondly and more important,

If I had a file

let's call it demo

how quickly can steam download it? :P

That depends on your internet connection and how many other people are downloading it.
I have seen Steam download things really fast on a 16MBit connection but some HL2 patches seem to take quite a while, possibly because half the world downloads them simultaneously.
In other words, if you do not tell anyone when they release that demo, and hope noone else notices, your chances to get a fast download are higher, your fame as the bringer of good news however, will be lower(you can still tell them once your download is finished, but someone else may have done it already by then).