我想通过DOS命令或者用vb写个程序把指定文件上传到公网指定的服务器。

用Inet控件吧，他可以帮助你完成你想实现的功能。
设置信息：
Inet1Protocol = icFTP
Inet1RemoteHost = ServerName'服务器地址
Inet1RemotePort = 21'FTP端口
Inet1UserName = uName'用户名
Inet1Password = uPWS'密码
下载文件：
Inet1Execute "", "GET 1txt d:\1txt"
ri = Inet1StillExecuting
Do While ri
ri = Inet1StillExecuting
DoEvents
Loop
上传文件：
Inet1Execute "", "PUT d:\1txt 1txt"
ri = Inet1StillExecuting
Do While ri
ri = Inet1StillExecuting
DoEvents
Loop

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