ERDAS should be faster for image processing, but if you want to do it in ArcMap it's pretty straightforward. Since you are trying to get both images to the same resolution, you would specify the path to the other image for the cell_size parameter. Depending on what classification your images fall under will determine the best resampling method to use.
Consult the help for a description of all this.
If you want to do this is in ERDAS, there is a tool (in 2011, it is located under Raster tab->Spatial->Resample Pixel Size) that I think is what you are looking for. From the help:
The Resample dialog resamples raster image data to a specified pixel size. Unlike Reproject, this dialog does not transform or project data from one map projection to another.