Newbe PC audio

Lots of possibilities. The best, but expensive option would be the Empirical Audio stuff. Alternatively you can go with a DAC that already looks after the jitter issue to a decent degree such as the Benchmark. Unfortunately the sterile DAC-1 probably wouldn't be to your liking (it's not to mine). I have a Paradisea+ tube DAC connected to my Vista desktop via a FOCUSRITE SAFFIRE Le.

http://www.focusrite.com/products/saffire/saffire_le/

True, but then you need to compare the DAC-1 to units costing three times as much that may sound as good or better without all the tweaking.

While firewire is preferable to USB I wouldn't say a "world of difference". Enough though for me to choose a firewire product in the Saffire LE.