Post File From Server To Another Server

I accept a few user inputs and a file from the user, post it to my ASP page.
I'm able to receive the data as well as the file properly in Receiver.asp.
In my receiver.asp, I need to process the user inputs and subsequently POST
this data and the file again to a different server. I would like to use
ServerXMLHttp. Now, how do I simulate Form creation in receiver.asp.

I use the following code to post to the second server
MyXmlHttp.open "post", myTargetURL,false
MyXmlHttp.setRequestHeader "Content-Type", "multipart/form-data"

Now here's where I get stuck.

1) How do I construct the form data? How can I put together the data i
received (which is text) as well as the received file (which is Binary) in
the same Send statement for the Post? -- I assume that if HTML forms do it in
some format, I should be able to simulate the same through ASP, but how???

2) The received file will not be stored anywhere in my server. It has to
be forwarded in memory.

Should it look somewhat like the following?

MyXmlHttp.send ("userId=" & someUserId & "&privateLabelID=" & someLabel &
"&File=" & receivedBinaryFileInMemory)