Saving files from post data via sys.stdin

[ACB]

I am rewriting an existing PERL script I wrote several months ago.  It is a 
script that is used as the action for a form containing several type="file" 
inputs.  The script is run unbuffered and writes the data from sys.stdin to 
a file which is stat'ed by another script called asyncornously from 
javascript.  In the end I am able to make a progress bar for file uploads 
via http.

Anyway, I have printed sys.stdin to a file and looked at it afterward.  This 
is what is looks like
-----------------------------126591649570
Content-Disposition: form-data; name="userid"

myUserid
-----------------------------126591649570
Content-Disposition: form-data; name="ulimage"; filename="bc12.jpg"
Content-Type: image/jpeg

binary data of jpeg
-----------------------------126591649570
Content-Disposition: form-data; name="ulimage"; filename=""
Content-Type: image/jpeg

-----------------------------126591649570
Content-Disposition: form-data; name="ulimage"; filename=""
Content-Type: image/jpeg


-----------------------------126591649570
Content-Disposition: form-data; name="sessionid"

mySessionid

Normally, I use cgi.FieldStorage() and access the values via calls like
form = cgi.FieldStorage()
sessionid = form["sessionid"].value

What is the best method for accessing the various variables and their 
respective values so I can save the files one at a time?  Is there some 
class that can take this input and make it easier to deal with?  I need to 
save each of the ulimage values as individual images and gain access to the 
values of sessionid and userid.

Thanks
Amy