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