when I try to play a hulu video it tells me that I need to install a flash plugin that I already have installed,
Open the ~/.huludesktop configuration file and manually input the path of libflashplayer.so in the flash_location line.
Like in My AntiX install. To find libflashplayer.so location path
$ locate libflashplayer.so
I am not on my Desktop that runs Miro so I can't help with that at the present time. You might want to see if there is a ~/.miro config file and see if it needs the same as hulu.
I know hulu desktop leaves that line blank with "" for flashplayer=. I don't remember with miro though.