How best to back up my iPhotos before erasing internal drive?

To backup your photos you simply export them from iPhoto to a folder and backup that up

To backup your iPhoto library (which includes your photos in two ro three versions), editing information, events, albums, projects and many other things you must backup the entire iPhoto library as a single entity

My iPhotos are divided between the internal drive and an external drive which currently works with Time Machine.

This does not make any sense - what eactly are you saying? do you have a default "managed" library (the iPhoto preference to "copy imported items to the iPhoto library is in its checked state) or a referenced library (you hae unchecked this preference? It is not possible to have the iPhoto library divided between two different disks

And you shoujld not have the iPhoto library on the same volume as the Time Machine backup

However I am unlikely to use TM in future if, as I understand, it only works by backing up the entire system rather than just selected files.

And again this makes no sense

First you certainly need to backup everyhing up - if you do not you will lsoe it sooner or later

second TM does do a total backup the first time but after that it only backs up what has changed

thrid - you can select exactly what it backups in the TM preferences - but again you really need to have at least one total backup constantly (I have three)

I would like to keep my photos organised by date so should I copy the entire iPhoto folder, including all the .data, etc files, onto the external drive?

In iPhoto you organize using iPhoto - you do not organize the files - if you want a file manager rather than a photo manager then you need to use a different program

LN

A drive may have mutiple volumes on it by partationing it

By the Time Machine backup I mean the backup being made by the Time Machine backup application - if you want to use Time Machine (which I personally use and recommend) it needs a dedicated eternal hard drive - you ned a second hard drive for any other files

LN

you can do what you want - it is not a good idea to have a Time Machine backup on the same volume with any other dynamic files since TM continues to add to its backup until the volume is full at which point other files will not be able to be written adn will fail

Again I personally use and recommend Time machine backing up everything along with a second bootalbe clone done daily - I consider my files and photos valuable and therefore have those two daily backups plus an occassional off site backup

LN

Not at all

Yes you can create two (or more) volumes on an external drive

No you can not have Time Machine backup up the OS to one volume and files to the other

Dynamic files - files that are dynamic - they change - the are not static

Bootable clone - a clone that can be booted - if your ard drive fails you can simply boot up the bootable clone and everything is exactly as it was when it was made

Back to your original question

The best way to backup your photos before erasing your hard drive is to make a copy of the iPhoto library on a volume that does not also contain the time machine backup

as to using Time Machin see http://support.apple.com/kb/HT1427?viewlocale=en_US&locale=en_US - and note that the volume that you use for your time Machine backup should have no other files on it and should be at least 1 1/2 times the size of your main drive and 2 1/2 times as large is better

LN