可以用流下载(耗内存，少用)或直接转到该文件.
<%
Const USE_STREAM = 0 '0.不用流(Adodb.Stream)下载 1.用流下载
Const ALLOW_FILE_EXT = "rar,zip,chm,doc,xls,swf,mp3,gif,jpg,jpeg,png,bmp" '允许下载的文件的扩展名，防止源代码被下载
Dim sDownFilePath '下载文件路径
sDownFilePath = Trim(Request("FilePath"))
'或者根据传过来的文件ID从数据库中获取文件路径
'如果 sDownFilePath 为绝对路径，一定要将 sDownFilePath 转换为相对 本文件的相对路径
'sDownFilePath = "focus.swf"
Call DownloadFile(sDownFilePath)
Function DownloadFile(s_DownFilePath)
'判断有没传递文件名
If IsNull(s_DownFilePath) = True Or Trim(s_DownFilePath) = "" Then
OutputErr "错误：先确定要下载的文件，下载失败"
End If
'判断扩展名是否合法
Dim s_FileExt
s_FileExt = Mid(s_DownFilePath, InstrRev(s_DownFilePath, ".")+1)
If InStr("," & ALLOW_FILE_EXT & ",", "," & s_FileExt & ",") <= 0 Then
OutputErr "错误：文件类型（" & s_FileExt & "）不允许被下载，下载失败"
End If
s_DownFilePath = Replace(s_DownFilePath, "\", "/")
'为了安全，某些目录禁止下载文件，在这里处理
'
'检测服务器是否支持fso
Dim o_Fso
On Error Resume Next
Set o_Fso = Server.CreateObject("Scripting.FileSystemObject")
If Err.Number <> 0 Then
Err.Clear
OutputErr "错误：服务器不支持fso组件，下载失败"
End If
'取得文件名，文件大小
Dim s_FileMapPath
Dim o_File, s_FileName, n_FileLength
s_FileMapPath = Server.MapPath(s_DownFilePath)
If (o_Fso.FileExists(s_FileMapPath)) = True Then
Set o_File = o_Fso.GetFile(s_FileMapPath)
s_FileName = o_File.Name
n_FileLength = o_File.Size
o_File.Close
Else
OutputErr "错误：文件不存在，下载失败"
End If
Set o_Fso = Nothing
'判断是否下载的文件大小超过限制
'
'如果不是用流下载，直接转到该文件
If USE_STREAM = 0 Then
Response.Redirect sDownFilePath
Response.end
End If
'检测服务器是否支持Adodb.Stream
On Error Resume Next
Set o_Stream = Server.CreateObject("Adodb.Stream")
If Err.Number <> 0 Then
Err.Clear
OutputErr "错误：服务器不支持Adodb.Stream组件，下载失败"
End If
o_Stream.Tyep = 1
o_Stream.Open
o_Stream.LoadFromFile s_FileMapPath
Response.Buffer = True
Response.Clear
Response.AddHeader "Content-Disposition", "attachment; filename=" & s_FileName
Response.AddHeader "Content-Length", n_FileLength
Response.CharSet = "UTF-8"
Response.ContentType = "application/octet-stream"
Response.BinaryWrite o_Stream.Read
Response.Flush
o_Stream.Close
Set o_Stream = Nothing
End Function
Sub OutputErr(s_ErrMsg)
Response.Write "<font color=red>" & s_ErrMsg & "</font>"
Response.End
End Sub
%>
http://www.cnblogs.com/jiny-z/archive/2006/08/29/489102.html