The file of the descriptions is a bit scruffy atm, i will tidy it up and post it again soon here. (scruffy file attached to this post, you need to be logged into the forums to dl'ed it)
the path to the m500 ext rom is ..... i cant connect to the ftp atm.
I backed up the ext rom on my desktop pc, and put the vital cabs on a sd card that i have spare and keep in my wallet, just incase the rom resets.
I had a similar problem to dan13l when i dumped the rom, the ntrw.exe app is a bit of a pig, as it dumps a image of the sd card, and not of the actual rom.... i used a 256mb card, i suppose you could partion the 1gig card to around 256mb then try it out?
something that i didnt read was, when performing the rom dump, is that the sd card will be fully erased during dump. So back it up if you need the data on it.
one word about one of the cabs in the ext rom, OrangeUK_ActionE_Connection.cab is a odd one. It encloses some apps that i didnt like installed on my m500 but it has the gprs settings inside it, i have managed to pull these out and put them in there own cab. This helps prevent installing the annoying "action" programs