Forgive me asking a very basic question but what do you want the external sound card for? Is it to get sounds onto your laptop or to improve how you hear the sounds? Framkly, if the latter you'd get much better value from decsnt loudspeakers before it's worth getting the sound card. From what you've said you have the material you want to esit using Vegas Pro on your computer already. So all this material is in the digital domain. If ypou want to mix or apply effects, this will be done digitally using software. Mixing and mastering will also be done in software.

However, if you are using the laptop to record live music, say, especially if it's to in-sync with a backing track played by your computer, then an external sound card with low latency will be what you need. Creative - possibly their professional seriex, M-Audio or Asus are brands to look at.

Yes you are right.

the only reason you might need a high quality external sound card is to convert analogue sound - eg from a microphone - to digital, or output from digital to an analogue medium such as speakers.

That said, you can get micropones that plug into USB (they have a little analogue to digital converter built in), and you can get speakers that plug into USB too.

As an example, I have an external sound card that I use to connect to an old vinyl turntable so that I can convert LPs to mp3, or old tapes. My laptop doesn't have a line in socket!