以下代码如何修改,才能限制上传文件类型?

<% 
Dim FormData, FormSize, Divider, bCrLf 
FormSize = Request.TotalBytes 
FormData = Request.BinaryRead(FormSize) 
bCrLf = ChrB(13) & ChrB(10) 
Divider = LeftB(FormData, InStrB(FormData, bCrLf) - 1)

Function SaveFile(FormFileField, Path, MaxSize, SavType) 
Dim StreamObj,StreamObj1 
Set StreamObj = Server.CreateObject("ADODB.Stream") 
Set StreamObj1 = Server.CreateObject("ADODB.Stream") 
StreamObj.Mode = 3 
StreamObj1.Mode = 3 
StreamObj.Type = 1 
StreamObj1.Type = 1 
SaveFile = "" 
StartPos = LenB(Divider) + 2 
FormFileField = Chr(34) & FormFileField & Chr(34) 
If Right(Path,1) <> "\" Then 
Path = Path & "\" 
End If 
Do While StartPos > 0 
strlen = InStrB(StartPos, FormData, bCrLf) - StartPos 
SearchStr = MidB(FormData, StartPos, strlen) 
If InStr(bin2str(SearchStr), FormFileField) > 0 Then 
FileName = bin2str(GetFileName(SearchStr,path,SavType)) 
If FileName <> "" Then 
FileStart = InStrB(StartPos, FormData, bCrLf & bCrLf) + 4 
FileLen = InStrB(StartPos, FormData, Divider) - 2 - FileStart 
If FileLen <= MaxSize*1024 Then 
FileContent = MidB(FormData, FileStart, FileLen) 
StreamObj.Open 
StreamObj1.Open 
StreamObj.Write FormData 
StreamObj.Position=FileStart-1 
StreamObj.CopyTo StreamObj1,FileLen 
If SavType =0 Then 
SavType = 1 
End If 
StreamObj1.SaveToFile Path & FileName, SavType 
StreamObj.Close 
StreamObj1.Close 
If SaveFile <> "" Then 
SaveFile = SaveFile & "," & FileName 
Else 
SaveFile = FileName '显示出的文件名 
End If 
Else 
If SaveFile <> "" Then 
SaveFile = SaveFile & ",*TooBig*" 
Else 
SaveFile = "*TooBig*" 
End If 
End If 
End If 
End If 
If InStrB(StartPos, FormData, Divider) < 1 Then 
Exit Do 
End If 
StartPos = InStrB(StartPos, FormData, Divider) + LenB(Divider) + 2 
Loop 
End Function

Function GetFormVal(FormName) 
GetFormVal = "" 
StartPos = LenB(Divider) + 2 
FormName = Chr(34) & FormName & Chr(34) 
Do While StartPos > 0 
strlen = InStrB(StartPos, FormData, bCrLf) - StartPos 
SearchStr = MidB(FormData, StartPos, strlen) 
If InStr(bin2str(SearchStr), FormName) > 0 Then 
ValStart = InStrB(StartPos, FormData, bCrLf & bCrLf) + 4 
ValLen = InStrB(StartPos, FormData, Divider) - 2 - ValStart 
ValContent = MidB(FormData, ValStart, ValLen) 
If GetFormVal <> "" Then 
GetFormVal = GetFormVal & "," & bin2str(ValContent) 
Else 
GetFormVal = bin2str(ValContent) 
End If 
End If 
If InStrB(StartPos, FormData, Divider) < 1 Then 
Exit Do 
End If 
StartPos = InStrB(StartPos, FormData, Divider) + LenB(Divider) + 2 
Loop 
End Function

Function bin2str(binstr) 
Dim varlen, clow, ccc, skipflag 
skipflag = 0 
ccc = "" 
varlen = LenB(binstr) 
For i = 1 To varlen 
If skipflag = 0 Then 
clow = MidB(binstr, i, 1) 
If AscB(clow) > 127 Then 
ccc = ccc & Chr(AscW(MidB(binstr, i + 1, 1) & clow)) 
skipflag = 1 
Else 
ccc = ccc & Chr(AscB(clow)) 
End If 
Else 
skipflag = 0 
End If 
Next 
bin2str = ccc 
End Function

Function str2bin(str) 
For i = 1 To Len(str) 
str2bin = str2bin & ChrB(Asc(Mid(str, i, 1))) 
Next 
End Function

Function GetFileName(str,path,savtype) 
Set fs = Server.CreateObject("Scripting.FileSystemObject") 
str = RightB(str,LenB(str)-InstrB(str,str2bin("FileName="))-9) 
GetFileName = "" 
FileName = "" 
For i = LenB(str) To 1 Step -1 
If MidB(str, i, 1) = ChrB(Asc("\")) Then 
FileName = MidB(str, i + 1, LenB(str) - i - 1) 
Exit For 
End If 
Next 
End Function