smileyc 0 Newbie Poster

Hi. I am using visual studio 8, using vb.net. I am trying without success to make a post request to a web form as shown below.

<?xml version="1.0" encoding="UTF-8"?><postBetOrder xmlns="urn:betfair:games:api:v1"marketId="2568540" round="1" currency="GBP"><betPlace><bidType>BACK</bidType><price>2.5</price><size>2.50</size><selectionId>658440</selectionId></betPlace>

I encode the information using 'HttpUtility.UrlEncode' and I use
'myWebRequest.ContentLength = bytedata.Length' to get the length and then I use

postStream = myWebRequest.GetRequestStream()
        postStream.Write(bytedata, 0, bytedata.Length)

to post, but keep getting a 'premature end of file' error.
I dont think that I am posting the right information. Am i supposed to post just the information or do I post the the tags and the information? This is all very new to me and I really am stuck so if anyone can help I'd be most grateful. Thanks for all and any contributions.