Be sure to have a decent microphone.

The sound card in the computer can make a difference also- I had 2 that did not pick up any mic sounds very well at all.

If buying a new computer - ask if the sound card, or on board sound is high quality - because you will need to use voice recognition at times.
It wouldn't hurt to ask about testing it at the store to see if it seems to fit your needs.

I was looking for more info and did see that Vista does have a voice recognition built in or added on to it - so you might ask for a demo of it at the store too.
http://www.microsoft.com/enable/prod...ta/speech.aspx

I used this one yrs ago and it worked fine -
http://ivos.comunx.com/