Whoa hang on there. Do you have one of those MIDI guitars?
It sounds like you're using the term MIDI wrong. MIDI has no sound, it's just messages passing between devices.
Most soundcards have MIDI input ports, and you can, for instance, hook a MIDI keyboard up to your soundcard and use it to play soundfonts on your Soundblaster Live! Value. NO SOUND passes between the two though, MIDI messages are sent to the soundcard instructing it to, for instance, play a particular sound.
You want to somehow record your guitar. In order to record your guitar, you either need to run some sort of guitar preamp device (like a POD or JStation) into the line in port of your soundcard, or use a microphone and mic your amp.
A dynamic microphone like the Shure SM57 is a good starting point for mic'ing an amplifier, and you can technically plug it in to the mic in port on your soundblaster. It is recommended, however, that you eventually get a decent microphone preamp...but it depends on your needs, and we don't know your needs yet. A mixer in this case would only be useful because they typically have built in microphone preamps. See a microphone outputs a very low level signal, so you need what is called a "preamplifier" to amplify the low level signal to line level. This process is, as odd as it may seem, VERY important to your sound quality. The MIC IN port on your soundcard has a cheap little microphone preamp built in.
External soundcards and internal soundcards are for all intents and purposes the same exact thing. A soundcard is basically just an A/D/A converter, in that it converts analog signals coming in to 1's and 0's that the computer can understand, and also converts those little 1's and 0's back into analog sound that you can actually hear.
So anyway, anything that has a LINE level output can be plugged into the LINE IN port on your soundcard and you can record it. You can hook either a computer microphone or a dynamic microphone into the MIC IN port on your soundcard. MIDI devices can be hooked up to the MIDI/joystick port on your soundcard. Once you get a handle on these simple concepts, you should be able to at least get started.
Good luck to ya!
Slackmaster 2000
