i was wondering if it is possible to plug a guitar into a sound card and effectivly use your pc as an amp. if this is possible, which sound card would be best to use or is there an adapter of some sort?
You could plug in the guitar in Line-in (or Mic) input on your soundcard and you're ready to go.
But the guitar's signal is weaker than a regular preamplified signal, so to avoid background noise you'll need a soundcard with good signal/noise ratio.
Also, make sure that the capture software you're going to use is of a decent quality. Something that should also be able to boost the signal from the guitar, since like Lorand said, the signal is going to be very weak (why they use shielded cables for guitars )
Here are more instructions on this: http://www.geocities.com/guitarfx_2001/
From there you could even download a software which adds effects to the guitar sound.