MIME decoding

I have looked back into some related topics on MG but I have not found an answer to this. When some people send me attachments, they arrive with no file extension. When I download them and try to open them, or try to open them from the email client (I use gmail), of course XP asks what program I want to use to open them since they have no extension. I have tried IzArc to no avail. Using Notepad to open the file as text, I see the header informarion that indicates it is a multipart MIME message, blah blah. Then it goes to all binary. From talking to the people that send these, they are typically .jpg or .gif files, but apparently when generated on their end from Outlook or Outlook Express, they end up as attachments in gmail with no extension.

I have looked here for anything that claims to be a MIME decoder. I can't find anything. I am sure there is a way to determine what type of files are contaiined in the message, or maybe I can find a workaround where I can cut the actual binary and paste it into a file to be opened by a .jpg or gif viewer. What obvious thing am I missing?

Thanks.