In Poser 7, is there any way to easily add numbers or text on top of textures?

Also, if I want to make it look like there is a hole in the ground, it will leave the hole among the GROUND object, is there any easy way to cover the space around the hole?

I believe your are looking to decal within Poser as opposed to adding your number or text  to the original texture in a 2D program.  Here are 2 tutorial links on how to address it:

http://artzone.daz3d.com/wiki/doku.php/pub/tutorials/poser/poser-maps05

http://www.superheroinecentral.com/mrx/xpage/decaltutorial/decaltutorial.htm

Can't answer your second question, but some one more familiar with the process may elaborate.

you could use something like the Gimp (do a search on 'the gimp').  works like Photoshop, costs like sunshine...;)

You can save the picture, then import it into anything that can do layers.

I wish I'd said that.. The Staircase Wit

anahl nathrak uth vas betude doth yel dyenvey..;)