Mixing desks

Don't plug your mic straight into the computer. It will sound bad!

Get yourself a mixing desk, preferably one equipped with phantom power (this enables you to operate powered condenser mics - the desk will have a button for this purpose, possibly saying '+/- 48v' - the voltage used to work the microphone). A desk will not only provide an interface so you can get the best out of your mics, you can have more than one mic in use, and even record in stereo (even a basic soundcard will allow you to do this - and it also means you can record vocals onto one track, guitar onto another as left and right inputs, and then simply change them back to two mono tracks - neat trick, huh?). There are plenty of affordable small mixing desks out there. The simpler the better, as long as it has phantom power. My own preference is for the Yamaha MG-10/2 and its associated models (because I have one and it works!) - but look around, and there are plenty of other manufacturers doing similar things. You don't need to spend a lot.

You can also buy recording pre-amps, which fulfill a similar purpose, and are good for boosting direct line inputs from electro-acoustics and dynamic/passive mics. However, these are limited in terms of wider use for recording from more sources, and no cheaper than a desk. Keep your options open!