Oke well first of all you can't just inject an packet cause silkroad has some security bytes. So you would need some kind of proxy to control the packets between the server and client. drew benton wrote a silkroad security code which is a few threads under this one which you absolutly need.
btw If you've never worked with some kind of network thing I wouldn't recommend you to just start writing a bot but to first start to get comfortable with the whole proxy idea and write a good packet parser ect.