Hi

More info needed from you!

what mics are you using? "semi-decent condenser mics" doesn't really tell me anything. Mics have different sounds. For instance, the AKG C4000B is a decent condenser mic, but it has a very dark, boomy sound to it. It wouldn't do justice to, say, a mandolin or banjo in my opinion. That's why I recently upgraded to an AKG C414B XLS. (Which you can put basically anywhere and it will sound brilliant. And it's totally noiseless)

I second all recommendations on mic placement. Try everywhere. Different heights too. I sometimes record guitars with the mic not even in front of the guitar: sometimes positioning the mic in basically the same place as your ears pays dividends. (It is after all, the position you yourself hear your guitar from)

Stupid question, I know, but you are supplying phantom power to the mic, right? Does it have switchable settings (omni/cardioid etc)? Does it have a bass roll-off switch?

As far as computer noise goes, I can recommend buying an Apple Mac. My iBook is silent as the grave. And portable too. When I run out of hard drive space on it I back-up to a USB hard drive. For editing I plug in a larger monitor to spare my eyes staring at a teensy screen. (Though I'm thinking of gettting a Mac Mini anyway). For anyone yet to invest in a computer for recording acoustic instruments at home, i'd recommend getting a mac.