Depending on your particular usage for a sound card, "latency" may be a concern, especially when using a software synth. Latency is a delay between the time the computer gets a message to play something and the time your sound card delivers it.

For just playing MIDI files, all that occurs is a practically unnoticeable additional pause before the piece starts playing. However, for live keyboard usage (including recording), it may become a significant issue. Here's a web page that explains latency: http://www.pcmus.com/latency.htm

A Google search on "sound card latency" will turn up quite a bit more.

--Barry