Take your cursor as close to the edge of your image as possible without going over the edge and single left click.

Keep on making these "marks" with your left click until you've got a small section of your picture traced with your tool.

Take your cursor back and make the 2 ends meet (making "marks" as you go if you need to) then single right click.

This is what I've got for my first section of my picture (I've zoomed in to show more detail):

Which is a really zoomed in part of this section of my image:

Not all the sections on your image are going to be this small... the next one up is going to be a lot bigger, but this is what you should be aiming for on all your sections... the selected bit should be the background, not the image and the selection should be as close to the edge of your image as possible for a nice crisp tube  :o)

Now hit "delete" and that section disappears from your image!  Woohoo!!  You've just made a start on your tube!  

Now zoom in on your image to the bit you've just deleted and check to see if there are any bits that shouldn't be there... any remains of the background you've just taken out or whatever:

On mine, I've got that line down the outside left over from the background... I need to get rid of that to make a nice crisp, clean tube.

Use your eraser tool with the following settings and take that line out pixel by pixel:

Shape:  Square
Size:  1
Hardness:  100
Opacity:  100
Step:  25
Density:  100

This is what mine looks like now:

If you've got any parts around the outside of your image that are out of place... they're too dark or too light in comparison to the rest of the pixels in that area, just lower the Opacity setting and single left clicking on the pixel until it blends in better.  The lower the opacity setting, the more transparent the pixel will be when you click on it.

When you are happy that this section of your image is nice and clean, Deselect (Selections, Select None or Ctrl+D if you like keyboard shortcuts)

Save

Now keep on repeating these steps for the other sections on your tube... make the sections as small or as big as you are comfortable with, but remember, if you make a mistake, the only way to get rid of it is to start on that section again so be careful not to go too wild and make your sections too big!  :o)

Don't forget any little details too - like the inside of the halo etc on this image!

Remember to keep on saving!!

If I were you, I'd take a break from the computer, just for a few minutes, when you are quarter, half and three quarters of the way around your image... just so that you can give your eyes a bit of a break and you don't get too frustrated.

Here's what mine looked like when I took my breaks:

         

That's it!  Just save your image as a .psp file and you're finished!!  :o)