There are several other options as well, that differ from the above mentioned ideas, but I think our understanding of what you are doing differs, hence the differing suggestions.
You could download the MJ Webremote plugin, and use it for controlling what music is played on the server. This is a simple web based tool.
You could in addition to the MJ Webremote plugin, download Glissando. This is a flash player, that connects using the MJ Webremote functionality, but adds some things to the GUI. This also can be used directly from a Web Browser.
You could use something called Net Remote. I can't add anything beyond that, since I have not worked with it.
Any of these methods can be searched for in these forums, and you should be able to find the necessary info to get you started. Personally, I use Glissando, from a Laptop in my Kitchen, to control my "server" down in the basement, that is sitting next to my home stereo that is wired in to all the speakers in my house. I control that home stereo using a remote extender that I bought at Best Buy for $50. It turns the stereo on and off, and all I have to do is control MJ remotely using Glissando. Hope this helps some
Drew