Well, the Conn variable is an object, so to set a value for it (or because it's an object a reference to a value) you need to use the Set keyword:
I would strongly suggest that you use the Access OLEDB provider instead of the native Access driver. It doesn't make things any more complicated, it's probably a better choice performance-wise too (although if you're using Access you can't really expect much in that respect) and if you ever need to port your code to use a proper database system, you won't have to make any changes to your code (other than changing the OLEDB provider declaration).
Set Conn = Server.CreateObject("ADODB.Connection")
Use the INSERT SQL statement (as in norie's answer) instead of creating a recordset. It's faster and makes more sense. The downside is that it's also vulnerable to SQL injections, so make sure the form fields do not contain any SQL commands, if the form is accessible to all.
Don't use reserved words (in this case day, month, year) as table field names. Your queries will not work, if you do.
When you load the page from the web server, the web server has to be able to access the physical file and have the right to update it. So make sure the user account that the web server is using for anonymous access (unless your site uses some sort of an identification method) has write permission to your main.mdb file.
One more thing. Using dates with the INSERT statement can be a pain, because you always have to use the right date format. In your case, since you're inserting the current date/time, let Access deal with it. Change the design of your updates table so that the when field has a Default Value of Now(). You could do a similar operation to your day, month, and year fields (or item_day, item_month, and item_year as they are in my example).
So here's the actual code that I got to work. It has a addNewsItem function with the news title and body as it's parameters. It also has an error message parameter that you can display to the user, if the function returns false (i.e. fails to update your database). Ideally you'd have the function in one file that you include to the file where your form is, but for simplicity I've got the function and it's caller in the same file.
If (addNewsItem("My headline", "And the news body", strErrorMessage) = True) Then
Response.Write "Hey it worked!"
Function addNewsItem(strTitle, strBody, strErrorMessage)
On Error Resume Next
Set objConn = Server.CreateObject("ADODB.Connection")
objConn.Mode = 3
strSQL = "INSERT INTO updates (title, body, item_day, item_month, item_year)"
strSQL = strSQL & " VALUES ("
strSQL = strSQL & "'" & strTitle & "', "
strSQL = strSQL & "'" & strBody & "', "
strSQL = strSQL & DatePart("d", Date()) & ", "
strSQL = strSQL & DatePart("m", Date()) & ", "
strSQL = strSQL & DatePart("yyyy", Date())
strSQL = strSQL & ")"
If (Err.number <> 0) Then
strErrorMessage = Err.Description
addNewsItem = False
addNewsItem = True
Set objConn = Nothing
On Error GoTo 0