[CentOS] Upgrading Drive, Best Practice?

Hi,

This might sound like a n00b question, but I've honestly never done this 
with a Linux machine...  (it is running Centos3)

We have a 1U mail server with two 36GB SCSI drives in a hardware mirror 
config.  There's no more room for any other drives in the case.  It's 
filling up, so we now have two 74GB drives ready to take their place.

Possible solutions that I've come up with:

1) shutdown all the services (postfix, courier, etc.) backup the machine 
to another box, swap out the drives, install CentOS4, copy the email 
back.  It's a pain, but I'd get a clean CentOS4 box when I'm done.  whee!

2) bootup with a bootdisk and use some kinda drive image utility to 
backup the machine (partimage, g4u, etc), swap out the drives, and then 
restore the image.  Less painful, but still running CentOS3 and I have 
to fumble around with those image utilities instead of good ol' 
tar-over-ssh.  :)

any others?

In the past I've usually just moved services from an old machine to 
another one.  So I had tons of time to configure/test the new server 
before making it live.  This one has to be done in place so time is of 
the essence.

How would you do it?

Thanks,
Ajay