Because speech requires a relatively low bandwidth, just about any
medium-high quality 16 bit sound card will get the job done. You must
have sound enabled in your kernel, and you must have correct drivers
installed. For more information on sound cards, please see "The Linux
Sound HOWTO" available at: http://www.LinuxDoc.org/. Sound card
quality often starts a heated discussion about their impact on accuracy
and noise.
Sound cards with the 'cleanest' A/D (analog to digital) conversions
are recommended, but most often the clarity of the digital sample is
more dependent on the microphone quality and even more dependent on the
environmental noise. Electrical "noise" from monitors, pci slots,
hard-drives, etc. are usually nothing compared to audible noise
from the computer fans, squeaking chairs, or heavy breathing.
Some ASR software packages may require a specific sound card. It's
usually a good idea to stay away from specific hardware requirements,
because it limits many of your possible future options and decisions.
You'll have to weigh the benefits and costs if you are considering
packages that require specific hardware to function properly.