USB to DAC questions

Well, yes I have gone through many stages of what route I think I want to go for my new system... coming all the way from using a Zune for a player.

Now, from doing some reading on here, it sounds like the cheapest way (im on a super budget) to get great sound from my computer is to either go with a squeezebox or run USB to a USB-DAC. I was sold on the squeezebox... but it looks like I could pick up a used DAC for about the same price and have superior sound quality. Err, a DAC would beat a squeezebox in full a/d mode, right?

Alright, so I feel loaded with questions about a computer hookup that I didn't see any clear-cut answers to...

First, when we are talking about hooking up a USB-DAC with a USB cable... are we talking about just running the cable straight from one of the built-in motherboard USB ports... or are we talking about running it out of some additional hardware like a sound card with USB out. From what is sounded like, it was just one of the stock USB ports... but I need to make sure of this.

Second, most people here seem to favor MAC to output their USB signal from. Buying another computer would be WAY out of my budget. I am planning on running it from my workstation PC which is running XP because all my editing programs in Vista ran terribly. Yet, dual-booting to Vista just to have good audio would be ok as I already own a copy. So... just to be clear, there would be a big difference between XP and Vista when running USB out? It would be ideal to NOT have to dual-boot... but I will if there is that big of a difference. Also, has anyone been able to compare Vista sound with Mac sound?

Third, can someone elaborate on the difference between a NOS DAC and an over-sampling DAC?

Fourth, how would the Outlaw RR2150 receiver with a built-in USB DAC compare to a separate USB DAC paired with a separate amplifier?

And the last that I can think of for now... Does anyone have any opinions of the Musiland Md-10 DAC? I only ask because there is one listed on here in the classifieds at a price close to what I want to pay.

Whew, ya that was a loaded posting. I hope you guys can help me out with these questions. Thanks a ton.