You can cycle thru all input tags and identify the relevant one by inspecting "the most identifying" attribute (id, name, type, innerHTML, ...whatever). Here's a Sub() I use in an Excel sheet which automatically logs on to a web site
Sub FormAction(Doc As MSHTML.HTMLDocument, ByVal Tag As String, ByVal Attrib As String, ByVal Match As String, ByVal Action As String)
Dim ECol As MSHTML.IHTMLElementCollection
Dim IFld As MSHTML.IHTMLElement
Dim Tmp As String
    Set ECol = Doc.getElementsByTagName(Tag)
    For Each IFld In ECol                                         ' cycle thru all <[tag]> elements
        If VarType(IFld.getAttribute(Attrib)) <> vbNull Then      ' does it contain the attribute
            If Left(IFld.getAttribute(Attrib), Len(Match)) = Match Then
                If Action = "/C/" Then
                    IFld.Click
                Else
                    IFld.setAttribute "value", Action
                End If
                Exit Sub
            End If
        End If
    Next
End Sub
The function takes following parameters:
- Doc .... the HTML DOM object
- Tag .... the tag you want to work on (usually input, image, a, ...)
- Attrib .... the attribute whose value you want to match
- Match .... the matching value for the attribute
- Action ..... if "/C/" the .Click() action is performed on the matched tag, else the action value is put into the value attribute of the tag
If you want to hook on any attribute containing JavaScript code (like "onclick") don't forget that the code you see in the HTML source is embeded in an anonymous function, like
function anonymous()
{
onclick="exportData(workOrderSearchForm)";
}
You need to consider this by using an Instr() function or similar, if you want to hook on e.g. "exportData(workOrder" .
Also very important: give enough time for the page to navigate to and for the DOM object to be loaded. I notice in my company that once pages are changed the loading times sometimes raise drastically. 
I have good success by this:
Sub MyMainSub()
Dim Browser As SHDocVw.InternetExplorer
Dim HTMLDoc As MSHTML.HTMLDocument
' my other Dim's
    ' start browser
    Set Browser = New SHDocVw.InternetExplorer
    Browser.navigate "http://www.whatever.com"
    WaitForBrowser Browser, 5           ' wait for browser, but not more than 5 sec
    ' gain control over DOM object
    Set HTMLDoc = Browser.document
    WaitForBrowser Browser, 5           ' wait for browser, but not more than 5 sec
    ' do actions
    ' FormAction HTMLDoc, w, x, y, z
End Sub
Sub WaitForBrowser(Browser As SHDocVw.InternetExplorer, Optional TimeOut As Single = 10)
Dim MyTime As Single
    MyTime = Timer                   ' seconds since midnight
    Do While Browser.Busy Or (Timer <= MyTime + TimeOut)
        DoEvents                     ' go do something else
    Loop
    If Browser.Busy Then
        MsgBox "I waited for " & Timer - MyTime & " seconds, but browser still busy" & vbCrLf & _
               "exititing Login sequence now"
        End
    End If
End Sub
Hope this is inspiring enough for you to create your solution.
Good luck MikeD