My hoster (ovh.com) use his own mirrors for debian.
so here is my sources.list :

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deb ftp://mir1.ovh.net/debian/ lenny main contrib non-free
deb-src ftp://mir1.ovh.net/debian/ lenny main contrib non-free

deb http://security.debian.org/ lenny/updates main contrib non-free
deb-src http://security.debian.org/ lenny/updates main contrib non-free

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In this configuration, install.sh don't want to work. It ends with "Package webmin is not available".

So I change my sources.list in order to include official debian mirror :

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#deb ftp://mir1.ovh.net/debian/ lenny main contrib non-free
#deb-src ftp://mir1.ovh.net/debian/ lenny main contrib non-free

deb http://ftp.fr.debian.org/debian/ lenny main
deb-src http://ftp.fr.debian.org/debian lenny main

deb http://security.debian.org/ lenny/updates main contrib non-free
deb-src http://security.debian.org/ lenny/updates main contrib non-free

-----------------------------

right, the install.sh works now...

Whats wrong ? OVH's mirror seems to be 100% synchro with the Debian's one. I don't understand.
In addition, OVH customize Debian 32bit sources.list too. But there is no problem at install !!

Problem only in 64b... :-(