partman and Existing Partitions

[Youssef Eldakar]

Suppose I do the following:
 
d-i preseed/early_command string wget ftp://.../pt/pt-a -O /tmp/pt-a
d-i preseed/early_command sfdisk /dev/hda < /tmp/pt-a
 
How do I tell partman to format and use, for instance, /dev/hda5 for /, 
/dev/hda6 for swap, /dev/hda7 for /usr, etc.?
 
P.S. Where do I look for documentation on a package's debconf parameters?
 
Youssef Eldakar
Bibliotheca Alexandrina