I am of a similar mind to Bobbsy. I don't think the $100 pres are really much (any?) better than the small mixers. They're pretty much the same class of device - cheap, but usable. To improve meaningfully you have to spend a few hundred on a preamp.
One situation where a mic preamp would be better is if your soundcard was so crappy that you want to come into your PC via firewire or USB to bypass the soundcard. There are devices that do this as well. But if you go with the Emu or something like the M-Audio Audiophile 2496 that would not be an issue.
I think Bobbsy & others have you on the right track. There are other places on the web to learn, but keep in mind that audio geeks are particular and will suggest certain favorite gear and defend their choice to the death...
So be patient and take everything with a grain of salt (even me. Maybe especially me.
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