Migrate running IA32 system to Debian AMD 64?

[mailarch@archivum.info]

Hello,

I have a running critical production server, running Debian Sarge 32 Bits version.

I would like to migrate to Debian-AMD64 system, how can I do it, without interrupting for more
than 5 minutes my services which are running on it?

I mounted the ISO debian-31r0a-amd64-binary-1.iso at /mnt but I don't know how to start manually
the Debian installation program.
How can I start the install program manually?

I would like to install the Debian AMD64 distribution to a temporary device (USB key), then I do a chroot, if 
all works fine I will try to boot on the USB key, and then if all works very well, I will copy the USB key 
files to the old harddisk partition to complete the migration.

Is this possible?

-- 
Best regards,
saf