Image quality

[Mark-Gim]

A couple more questions:
A site that gives instructions for making t-shirts advises the following:

   Be at least 150 dpi
   Use CMYK colour mode
   Have a transparent background
   Have no effects like ‘Drop Shadow’ or ‘Glow’
   Have all types rasterized
   Saved as either EPS, PDF, PSD or PNG

It was my understanding from what Rich said that a .pdf file can't have a transparent background?
All of my .pdf files that were saved with transparent backgrounds show in viewers with a white background.
If they can't have a transparent background, why does this company recommend a trans. background AND
a .PDF file?

Also where do I go in GIMP to set the Type to be rasterized?