Ok. Just making sure you'd checked that out. 
I'd personally keep the mail script separate (I've marked in bold my changes):
Code:
<% @LANGUAGE = VBSCRIPT %>
<%
If request("action") = "register" Then
username=trim(request("username"))
strPassword = request("password")
strEmail = Trim(request("Email"))
%>
<!--#include file="inc-dbconnection.asp"-->
<%
Set Rs=server.CreateObject("ADODB.RECORDSET")
sql="SELECT * FROM members WHERE username='"&username&"'"
Rs.Open sql,objConn,1,3
If rs.EOF Then
rs.AddNew
rs("username") = username
rs("password") = strPassword
rs("sex") = request("sex")
rs("Fname") = Trim(request("Fname"))
rs("Lname") = Trim(request("Lname"))
rs("Email") = strEmail
rs("organization") = request("organization")
rs("location") = request("location")
rs("info") = request("info")
rs("info2") = request("info2")
If request("expertise_general") <> "" Then rs("expertise_general") = 1
If request("expertise_people_management") <> "" Then rs("expertise_people_management") = 1
If request("expertise_work_in_partnership") <> "" Then rs("expertise_work_in_partnership") = 1
If request("expertise_project_management") <> "" Then rs("expertise_project_management") = 1
If request("expertise_service_development") <> "" Then rs("expertise_service_development") = 1
If request("expertise_equality") <> "" Then rs("expertise_equality") = 1
If request("expertise_user_involvement") <> "" Then rs("expertise_user_involvement") = 1
If request("shadow") <> "" Then rs("shadow") = 1
rs.Update
rs.Close
Set rs = nothing
objConn.Close
Set objConn = nothing
'### send your mail here
Set Mail = CreateObject("CDONTS.Newmail")
Sender = "me@home.com"
Mail.From = "your.email@your.host, Your Name"
Mail.To = strEmail
Mail.Subject = "Thankyou For registering"
Msg = "Username: " & username & Chr(10)
Msg = Msg & "Password " & strPassword & Chr(10)
Msg = Msg & "Don't lose it!!"
Mail.Body = Msg
Mail.Send
Set Mail = Nothing
response.Redirect "thankyou_1.asp"
Else
response.Redirect "sorry_password.asp"
End If
Else
%>
<html> blah de blah </html>
<%
End If
%>
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