I'd go for a good internal sound card over an external sound card or USB speakers any day. USB sound is usually 100% software driven and the hardware there is usually cheap stuff.
Yes I would have to agree with Bill 100% there. Even the cheaper sound cards are usually better than the onboard chips and the USB.
Sure. I would probably agree with regards many products aimed at the home market.
The audio interfaces aimed at the home studio market come in a variety of shapes and sizes, including USB, Firewire and PCI-e and there are numerous configurations on the market. For the home studio market, I don't think their is a big difference in quality between the different interface types although I think there is a difference between manufacturers.
If you are really interested in this, you may like to research A-D / D-A converters to determine the best interfaces on the market.
I am sure you will be able to find information on this subject on the soundonsound website.
High end pro audio interfaces are generally PCI-e. This is due to the high bandwidth of the PCI-e bus which is required for data transfer of the audio interface and on board dsp.
