Regex

Hi First of all, thanks for this fabulous plugin. I need to change the following gallery image url's using regex replace. graphics/00000001/2/HH18T_150x150.jpg to mm5/graphics/00000001/2/HH18T.jpg I was able to replace graphics/ with mm5/graphics/ How would I replace the last part _150x150.jpg with .jpg or whatever file extension? Same question for the featured image. Thanks in advance