Welcome to Debian GNU/Linux sarge!

In addition to the default 'install' option,
there is 'install-safe' which you should try if
the system fails to boot at all (the typical
symptom is a white screen which doesn't go away).

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If in doubt, just choose 'install', and if that
doesn't work, try 'install-safe'.
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You may add the desired debconf priority after
'install', for example

boot: install DEBCONF_PRIORITY=medium

The default priority is high; medium priority
will result in a more 'manual' menu-driven
installer experience.