My friend,
Cloud removal in ERDAS is not complicated.
The ideea is to extract and mask the clouds using 2 images.
For example, you have a Landsat image with clouds in the left corner down, from august 2013. You search another Landsat image from the same area (june, july, september, etc) that has no clouds on the left corner down. Ok ?
So you first classify the clouds from the first image. Then clip that area or mask it. You overlay this image on the second image. The holes in the first image layer are filled with the pixels from the second image below.
Here you can find informations abouth this method:
http://geospatial.intergraph.com/community/forums/