backing up before debian install

[Tamas K Papp <tpapp@Princeton.EDU>]

Hi,

I am about to install debian on my g4 (alu) powerbook.  I would like
to have a dual boot system and if possible, preserve my current OS X
installation.  Two questions:

1. is it OK for debian and OS X if I just shrink the OS X partition
   using partman, and put an ext3 filesystem partition after it?  Or
   should I put it before, etc, or the whole thing is not relevant?

2. before using partman, I would like to make a backup of the whole
   disk.  What tools do you suggest for that?

   I can now boot the sarge netinstall cd (current, daily release) and
   mount partitions on my firewire/usb2 OWC 250 gb drive.  I thought
   of making a backup into a file on one of the partitions, using the
   tools on the sarge install disk.  Is this feasible?  What tools
   should I use?  I thought of dd, but I don't know how could I make
   it compare the data it has written with the disk, and I don't know
   which device name to use for the whole disk (not just a partition).
   If things don't work out, will I be able to restore from this?

Please share suggestions & ideas,

Tamas