Make sure you have the "Gutenprint Printer Drivers Package" and "GIMP plugin for gutenprint" installed (add/remove software, search for gutenprint)
A printer that uses a tray loading mechanism for printing disc media.
Open/create the image with the GIMP.
I find that an image size of 1394 x 1394 is ideal for normal size discs.
To create a working area in the image, first create a white circle.
To do this, use the circle selection tool and position the cursor at position 0,0 (top left).
Then, while holding the shift key down, hold left click and drag the cursor to the bottom right position, which should be 1394,1394.
Fill the selection with white colour.
Depending on the hub size of your disc you need to also cut out an area in the centre of the white circle approximately 22 mm in diameter. Position the circle selection cursor 11mm above the centre of the image, and 11mm to the left of the centre of the image. Then hold Shift down, hold left click and drag the cursor until the selected area is 22mm x 22mm. Then cut the selection.
Now create a new layer above the white circle and create your image, keeping inside the white circle and outside the centre "hole". If you are using non full face discs, make the centre "hole" bigger accordingly.
Create 2 new background layers, one black and one white. The black is so you can preview the image with the correct shape, and the white one is for use when exporting the final finished image for printing.
Remember to make the white layer above the black layer, or make the black layer invisible when exporting the image.
I have attached a template for your immediate use.
Once your image is finished, you should have a white square image, with your graphics arranged within a circle. White is not printed, so you don't need transparency around the edges. Don't put graphics too close to the edges of the circle or you will get ink on the plastic which never dries. (at least not until you have smeared it on your fabulous artwork ! )
Save the file as the default GIMP xcf format to preserve the layers then export it to png.
To print the image onto the disc.
With the image open in the GIMP,
In File > Page Setup
set the paper size to CD - 5 inch
Then go to File > Print with Gutenprint
Use the option to set up printer and find your make and model.
Once you have the correct printer selected, lots of extra options become available ;-)
My Printer settings are :
Print Quality - Best
Media Type - Photo paper
Media Source - Print to CD
CD hub size - Normal
Ink Set - Epson Standard inks
Resolution - 720 dpi
Ink Type - 6 color photo
Page Size - CD - 5 inch
(All the other settings are left as default)
On the Output tab there are more options for adjusting the print quality.
Just click "Adjust Output"
If you have adjusted the output, close that window then click "Print and Save Settings", otherwise just click "Print and Save Settings".
It should fire up straight away.
These settings are based on my Epson R200, so you may have to tweak them for your printer model.
Hope this is useful.