Suppose a person has three partitions on their harddrive: /, /home, /swap

Say Debian is installed in /, while all your personal files are sitting in /home. Can you simply install Slackware or whatever other distro in /, overwriting Debian but still preserving your files in /home?

sorry if this is a newb question, I'm just trying to figure out what exactly I need to backup if I decide I want to change distros at some point.

You could do it, but it won't work very well. It works fine for re-installing the same basic system, but with the different programs/versions/inherent differences in the distros your configs/profiles/etc are going to be off. I tried it with Mandriva 2009.1 when I upgraded to 2010 and tried to go back.......even that produced an unworkable situation that was just easier to restore from a backup.

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so I could at least safely upgrade my Debian to whatever new version happens to come out without any issues?

Maybe. I'm not sure about how Debian handles upgrades. For instance, when I updated from Mandriva 2009.1 to 2010 the upgrade didn't go so hot. Amarok got upgraded, the databases for the music directories between the versions weren't compatible and were overwritten. It's usually an iffy procedure to do in-place upgrades. Starting from scratch almost always results in a more stable system.

A better method might be to create a new partiton for data and mount it in something like /mnt/data. That way if you decide to do something drastic like upgrade or change distros (distro hopping is a hobby for some of us), then you can safely just format and install without having to worry about losing anything. I also make it a habit to leave unallocated space on a disk, for when I get into a situation where I have a lot of files and I want/need to move things around, or I feel like test driving a distro.

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What about changing from 32 bit to 64 bit of the same version? I currently have 32 bit installed because that was the only Debian disc I had when I got my new laptop, but I ordered the 64 bit dvd set, which I plan on installing when it arrives (I'm out of the civilized world right now and can't download things larger than 10 or so mb at a time).

Probably safe if the 32/64 is the only real difference. It's still a good idea to get some wiggle room on your system, especially if you are new to linux. People that are new to linux frequently do a lot of playing around before they settle down on a particular issue. It took me 4 months and 6 or 7 distros to decide on slackware for my main machine. Even with the extra partition I had some sticky situations when I decided to set a more sane partitioning scheme.

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