Most digital Multi-FX pedals have a line out mode or socket, which will make the guitar sound just as good throught line in when you set the pedal to line out mode. It''s to do with ipedance, whether you have a good software processor is not going to make a difference because guitar amps and pedals not normally output at the correct impedance for line level recording. DO NOT plug a guitar directly into a sound card with an active line in socket, you WILL destroy the pickups completely (especially electric, electro acoustic is normally okay as long as it doesn''t have magnetic pickups).

Many line ins on sound cards are active and pass current through them. Magnetic pickup become electromagnetic when you pass current through the coils, which causes distortion and will eventually burn them out. Pickups are passive electronics and the wire is so thin that passing even a small amount of current will fry a pickup. When you''ve got decent €200 pickups on your axe you do not want them fried.

Also, inputs have a certain impedance (resistance) on a line in I think it''s abot 300ohms for a microphone / line level device, guitar pickups are around 600. Which is why you can plug a guitar directly into a line level socket. You need a load balancer device to fix it.

Having said this, some guitar electronics are active, if you need a battery in your guitar. But it''s the impedance that matters then.

It can be bad, but you''ll probably just get a distorted sound. It''s all about impedance matching. Most line level inputs should be fine, the problem with computers is that many cards leak current becuase the inputs are not isolated with a transformer or opto isolator, some sound card also have active line in, which is very bad for guitars. You can''t plug a guitar directly into a PA system because PA is line level, so you need a box to match the impedance. the headphone output of a guitar amp can usually be plugged into a sound card directly, or mic the guitar amp (Again look on guitar sites) and plug the mic into your pc.

Look on guitar sites for information about how to do it right. Some sound cards do have guitar level inputs. If you''re really paranoid, plug the jack in and test the other end with an ammeter.

The main thing to remember is guitar coils act like a really low power electrical generator. If you''re wire a generator backwards it will fry the generator.

It''s the same reason a record player sounds really quiet if you plug it directly into a PC.

Mics that go to the input of computer sound cards are dynamic (passive) and basiclly work the same way a guitar pick-up works, cept a dynamic mic has a moving coil through a magnet field whereas a pick-up coil is stationary and moving metal (strings) changes the magnetic field inducing current into the coil.
Any voltage you may read coming OUT of the INPUT of a sound card will be DC (AC will be heard on the speakers). And if the voltage is "HOT" (i.e. level) enought to eventually fry your pick-ups, there''s something wrong w/your computor! (cause it would fry any dynamic mic too). People have been plugging in guitars (including myself) into soundcard since computers first came w/soundcards and I''ve never heard of one getting the pickups fried. And if you using any software the uses VST, then your probaly have a "Pro" soundcard and most of them are designed to except guitar input directly.
If you want to use you computer for realtime guitar playing, checkout SpinAudio. The have a freeware (ASIO Processor LE) that lets you use VST plugin in realtime.

www.spingaudio.com

Then go checkout this web site for cool FREE guitar amp and effects plugins!

http://www.simulanalog.org/guitarsuite.htm

But then the IMPEDANCE is not matched. Guitar coils have different impedance to mic and line inputs.

Consumer soundcards are all High Imp. inputs, which is about 10k, well high enough for most guitar pickups. Some active pickups are low imp., but you can "safely" feed a low impedance to a high imp. input, just don''t go the other way around (high -> low). The difference between high imped. line and high imp. mic is the voltage.
Most Pro cards for home studios have both high and low imp. imputs/outputs (1/4 imputs usually detect it by the type of plug you insert, either TRS or TS)and will have a trim/pad to ajust for line or mic level.
If you are using a consumer soundcard (the type w/1/8 imput/output jacks), you should be able to go into the mic input safely (although alot of pickup nowaday have pretty hot outputs, even the passive ones). Although using one of those "amp" modelers and going to the line input usually gives better results, even running clean, because of buffering.
Hope you guys chk''d out those websites I posted, you can get a really crankin'' sound outa your computer!

Ok right I didn''t know they were as high as 10K. I do stand by the fact that you cannot plug a guitar into an active line in without some kind of isolation.