CR2Builder is good for this. When you go to the page I linked to, click on "CR2Builder02m", then click on "CR2Builder02m12.zip Jan 22, 2007". Finally, on the Windows Live page, choose "CR2Builder02m12r.zip" to download the file. Extract it wherever you want.

To get rid of the unwanted material groups:

(1) In poser, go through and thoroughly confirm which ones you need to delete.

(2) RunCR2Builder.exe and open the prop file you want to edit (I'm guessing you saved them to the "Props" library), which will be in your Poser directory under "Runtimelibrariesprops". You should make a copy of the actual file and edit the copy.

If there is more than one "prop propname" item in the left pane, repeat steps 3&4 for each one.
(3) Click the [+] by "prop propname" to display the prop's components.

(4) I'm sure it'll be quite obvious what to do next, but just in case: select each "material" item that you wish to delete and hit the delete key on your keyboard. Once you are done deleting all of the unwanted materials, from the menu choose "LeftPage:Save" to save your file.

Today is a good day to...learn some advanced Poser tricks :-)