Those type of work can be done in Photoshop or GIMP or any other Graphics Editing software, Since GIMP is free to use , so that it is a good option. I think you can have little sprites of different shapes and size and then you can arrange them in C2 as per your need. Else you can also make one big terrain for one whole level. <img src="smileys/smiley1.gif" border="0" align="middle" />
If you need any help let me know for further help.
Thanks in advanced.
Bye bye take care.<img src="smileys/smiley4.gif" border="0" align="middle" />