If you do ping tests while downloading a file, you're also taking into account the possible latency created at your router/cable modem when they have to deal with a lot of packets. In the worst case, the ping packet can get dropped, but usually it's put in a queue and that delay is added to the ping times. The better modems/router use QoS to give priority to the more important packets, like UDP traffic for games or VoIP packets.
As for high/low, you want it to be as low as possible. A higher delay means your maximum speed using the TCP/IP protocol drops, especially if your internet settings in the registry are set up for low ping. For a real display of how good your router/cable modem is, try bittorrent at increasing percentages of your upload speed. Unless they're really good, you'll see ping spikes way before you saturate your upload link.