Wilcard info needed for directory datasource

I need to filter the following file set in the directory datasource - and only get the ones with _OK_ in them

if i put *.txt - i get all 3 but i only want the _OK_ ones.

I tried *_OK_*
and i tried *_OK_*.txt
both of these fail

Open to suggestions???


DITRexxx.txt_OK_AtSetup_request_03_13_2012 13_08_21.txt
DITRebbb.txt_OK_ActSetup_request_03_13_2012 17_11_01.txt
DITRebbb.txt_NO_ActSetup_request_03_13_2012 17_11_01.txt