I'm afraid that, as so often occurs, the answer is a definite "yes and know"
Originally Posted by ravenomega
The built in sound cards on pretty well any computer are built out of a few cents worth of parts and are very poor quality. What quality there is is aimed at the playback side so you can listen to DVDs or Youtube videos. The microphone input will be dreadful, aimed at Skype calls and so on.
Technically, you could get an adapter cable and plug a dynamic mic like the SM58 directly in--but it'll be unpleasantly noisy and, depending on the sound card in your computer, may be quite low in level.
it gets more complex with condenser mics like the AT2020 (and every other condenser). They require phantom power to operate and your in built sound card doesn't provide that.
Both these problems are easily solved with the addition of an external audio interface, probably connecting to your computer by USB. There are oodles out there but, if you are sure you'll only ever want a sing mic input, have a look at the M Audio Fast Track Mk.II. I'm sure others will be along soon with other suggestions.
The pessimist sees the glass as half empty. The optimist sees it as half full. The realist just drains the darn thing and gets a refill!