By Yngwie666
Two options:
1. Traditional way: put a SM57 microphone in front of your amp speaker and plug it into a mic preamp (for example a little mixer) into the LineIn of your sound card or try use the microphone input of your soundcard directly (but be aware that usually the mic preamp integrated into this kind of soundcard is very cheap).
2 Direct to PC: if you are using either a guitar preamp (Rocktron Chameleon is a good one) or a POD you can connect the output directly to the Line IN of your sound card.
In either case you have to set the level first. The easiest way is using a mixer with a Level meter: put the track in solo mode, fader in 0 position and slowly increase the gain so that the signal peaks is below red level. If this is done correctly then you know that the microphone signal is amplified to a line level and not already distorded (clipped) by the mixer.
Now you have to setup the level in (your software) in the same way. If the level is too high, the A/D converter of your soundcard will clip the signal and make some nasty distortion.
It should work with a SoundBlaster Live 24 but usually these cards have a slow latency (I haven't used SB for a few years now). This means that the card needs so much time to convert the signal from analog to digital that there is an annoying delay between the converted signal (your guitar) and the backing track.
More expensive cards have a shorter latency, better A/D converter, preamps are more transparent and usually have a Firewire port instead of USB but are much more expensive (SB Live24=20£, Presonus Firebox (I use this): 170£, Edirol Firewire: 179£, MAudio Firewire 410: 178£,...).
1. Be sure you have the latest drivers for your card. Download the latest versions from the manufacturer's site before you do anything else.
2. I'm assuming you're using Windows XP or Vista, then go on Control Panel -> Sound. There should be some sort of mixer (XP) or a Panel with Tabs (Vista). There are settings for Playback and for Recording, click on the "Advanced" button. Usually there is a checkbox somewhere labled "Mic boost" : uncheck this, otherwise you will always have an unwanted boost to your signal that might be the cause of the distortion.