No. Cookies, anonymous IPs, proxy servers, etc.; can all be manipulated. There is no way to prevent someone who isn't signed in from voting multiple times, unless you restrict voting to members only. That's an easy fix.
Look for the following lines (appx: 817-832), and delete the lines in red.
if Request.QueryString("poll") = "1" and (strRqMethod = "Topic" or strRqMethod = "EditTopic") then
Response.Write " <tr>" & vbNewline & _
" <td bgColor=""" & strPopUpTableColor & """ noWrap vAlign=""top"" align=""right""><font face=""" & strDefaultFontFace & """ size=""" & strDefaultFontSize & """><b>Who Votes:</b></font></td>" & vbNewline & _
" <td bgColor=""" & strPopUpTableColor & """>" & vbNewline & _
" <select name=""WhoVotes"" size=""1"">" & vbNewline & _
" <option value=""everyone"""
if strWhoVotes = "everyone" or strRqMethod = "Topic" then Response.Write(" selected")
Response.Write ">Everyone</option>" & vbNewline & _
" <option value=""members"""
if strWhoVotes = "members" then Response.Write(" selected")
Response.Write ">Members Only</option>" & vbNewline & _
" </select></td>" & vbNewline & _
" </tr>" & vbNewline
end if
Now, if you simply want to eliminate the bulk of anonymous/proxy users (it won't stop the really determined), you could do something like this. This does not set a cookie to indicate non-members have voted. That's another step.
Look for the following lines (appx 429-430):
'################################## Poll Mod #####################################
Select Case Request.Form("Method_Type")
Change those to say:
'################################## Poll Mod #####################################
strPollType = Request.Form("Method_Type")
ua = Request.ServerVariables("HTTP_USER_AGENT")
rp = Request.ServerVariables("REMOTE_PORT")
If rp > 9000 And rp < 9100 Then strPollType = "Proxy"
If InStr(ua, "Forwarded") Or InStr(ua, "Via") Or InStr(ua, "Proxy") Or InStr(ua, "forwarded") Or InStr(ua, "via") Or InStr(ua, "proxy") Then strPollType = "Proxy"
Select Case strPollType
Case "Proxy"
Response.Write "<p align=""center""><font face=""" & strDefaultFontFace & """ size=""" & strHeaderFontSize & """> </font></p>" & vbNewLine & _
"<table align=""center"" border=""0"">" & vbNewLine & _
" <tr>" & vbNewLine & _
" <td align=""center""><font face=""" & strDefaultFontFace & """ size=""" & strHeaderFontSize & """>Voting not allowed for proxy or anonymous connections!</font></td>" & vbNewLine & _
" </tr>" & vbNewLine & _
"</table>" & vbNewLine & _
"<p align=""center""><font face=""" & strDefaultFontFace & """ size=""" & strHeaderFontSize & """> </font></p>" & vbNewLine
WriteFooter
Response.End