Each package you selected with tasksel or aptitude is downloaded, unpacked and then installed in turn by the apt-get and dpkg programs. If a particular program needs more information from the user, it will prompt you during this process. You might also want to keep an eye on the output during the process, to watch for any installation errors (although you will be asked to acknowledge errors which prevented a package's installation). On iMacs, and some older Macintoshes as well, the X Server software doesn't calculate appropriate video settings. You will need to choose the Advanced option during configuration of the video settings. For the monitor's horizontal sync range, enter 59–63. You can leave the default for vertical refresh range. The mouse device should be set to /dev/input/mice.