You're talking about a laptop or desktop computer - not a bike computer, right? Zwift will record all of your data and send it to Strava so you don't need to a Garmin watch/bike computer to do that for you. Assuming I am correct, the most important component for running Zwift is the video card. On the suggestion from the great support staff at Zwift, I just purchased an Alienware Alpha. At less than $400, its about the cheapest computer you can find that will run Zwift at the top level. Its pretty great. I highly recommend. Good luck. Ryan
EDIT: And, make sure you buy a 6-10' USB extender so you can get the ANT+ dongle closer to you (for heart rate) and your bike (for speed/cadence and the power meter you will ultimately purchase).