How do I migrate my data from MacOS 9 to OS X?

Download http://a272.g.akamai.net/7/272/51/42d19360028364/www.apple.com/ pro/pdf/ L30290A_MigratingMacOSX.pdf for info. And/or follow these guidelines...
1) Your data files will be accessible almost exactly the same way you did in OS 9. So this part of the migration does not need to change. Just make sure you backup your important files, just in case.
2) Update the Mac’s firmware, see Installation Problems web page for details.
3) Format hard disk to HFS+, and partition the hard disk. May have to have a special (less than) 8gig partition on the hard disk in order for it to boot your old G3.
4) Update MacOS 9 to 9.1 (minimum) or preferably 9.2.2 - highly recommended.
5) Buy MacOS X versions of your software, so that you don’t have to keep using Classic mode all the time.
6) If you’re going to be upgrading to OS X on your current Mac, then backup your data in case the installation goes wrong. If things do go wrong, you may have to format the hard disk to redo the installation.

How do I move my data etc. from my old Mac to a new Mac?

Depends on what common connections you have on both Macs. If you have USB, Firewire or Ethernet built into your old and new Macs, then you're ready to copy your files. See how below:

1) FIREWIRE: Target Disk Mode - Boot up the old mac and hold down the T key to initiate Target Disk Mode on that Mac. Then a few seconds later after booting the old Mac, boot up the new Mac. The old Mac's internal hard disk should now appear on your desktop. Simply copy all of your files to your new Mac. When you're done, dismount the old Mac's HD from the new Mac's desktop and disconnect the Firewire cable.

2) USB - Buy/use a USB hard disk, that has enough space to take all of your data, or some of it at a time. Then connect it to the new Mac, and copy it to the internal/external hard disk.

3) ETHERNET Network - Nearly all Macs have an Ethernet port at the back, so if you're using a PowerMac that was produced before the blue and white G3s came out, then this is you're only option left to you, for direct copying of files. You will need to buy or borrow an ethernet cross-over cable, so that you can connect both Macs together successfully. Then once cabled up, go to the TCP/IP control panel/system preferences window, and setup a new configuration based on a manually set IP numbers. Don't forget that each Mac needs a different IP number, which is the last number. The IP number should have four sets of figures separated with 3 full stops, eg. 100.10.2.3. The last number is your unique number for your computer, the first 3 are for the network zone, so you must keep these the same on both Macs.

Other methods...

4) Use a backup program to save the files to a disk/tape that both Macs can use, then restore your data back to the new Mac's hard disk.

5) Copy to an internet/FTP site (with plenty of space on it), and download to new Mac - only if you have ISDN or Broadband, otherwise it'd be extremely slow process. You will also need to archive some files as MacBinary or stuffit files, to preserve the data/resource forks. Image files, such as GIF, JPEG, TIFF files should be OK as is, so long as they have .jpg, .gif, .tif, etc. added to the end.

6) Copy or burn to removable disks, eg. Zip disk, Jazz disk, DVD-RAM, CD-R/RW, DVD-+R/RW 'as is', so that it is backed up, and you can easily restore it to the new Mac's hard disk.

How do I move my data etc., from my PC to a new Mac?

You are limited to a number of different ways...

1) ETHERNET Network - Nearly all Macs have an ethernet port at the back, so if you're using a PowerMac that was produced before the blue and white G3s came out, then this is you're only option left to you, for direct copying of files. Otherwise you will need to buy or borrow an ethernet cross-over cable, so that you can connect both computers together successfully. Then once cabled up, go to the TCP/IP control panel/System Preferences window on the Mac, and setup a new configuration based on a manually set IP address. Don't forget that each Mac/PC needs a different IP number, which is the last number. The first three (eg. 100.10.2.3) represent the network zone, so you must keep these the same on both Mac and PC. Note, that MacOS 10.3 and above is the simplest OS to use, in order to connect to a PC without much fuss. See this picture.

2) USB/Firewire drives - Buy/use a USB/Firewire hard disk, CD-R/RW or any other type of disk media that both computers can access. Then it's a simple case of connecting it to the PC, copy your data, and then copy to the Mac, job done. This will only apply to Macs with USB or Firewire ports - only Mac G5s and Mac Mini's have USB 2 ports.

3) Backup your data - use a backup program or method that can be recognised by both types of computer. Retrospect Desktop (by Dantz) does not recognise backup sets created on a different type of computer - backup programs are not usually cross platform compatible. But you can use a third party computer to do the backup for you.

4) Copy to an internet/FTP site (with plenty of space on it), and download to the Mac - only if you have ISDN or Broadband, otherwise it'd be extremely slow process. I also suggest you archive some large files as Zip files, to lessen the time it takes to upload/download the file. Image files, ie. GIF, JPEG, TIFF files should be OK as is.

6) Copy or burn to a removable disks, eg. Zip disk, Jazz disk, DVD-RAM, CD-R/RW, DVD-+R/RW 'as is', so that it is backed up, and you can easily restore it to the new Mac's hard disk. Use the PC’s normal disk format, Macs can read virtually all types of PC formatted disks.

See the section How to connect to Macs and PCs over Ethernet for a fuller description of connecting over a network.