A-GPS = assisted GPS.
it will use telco cell to make the GPS lock faster if you turn it on.
GPS is still GPS, still using satellite to track you down.

if still confused, you can read detail explanation here: http://en.wikipedia.org/wiki/Assisted_GPS

i think u mean whether u can use the GPS without A-GPS .... ??

at least for the current android, you can turn off wifi/cell location services and it will purely depend on GPS for location services ... so most likely Nexus One would have this feature.