You need a network connection to deploy a channel to your Roku. You don't necessarily need to develop using the Eclipse plugin. You'll need a text editor (e.g. Notepad or Notepad++), a way to create Zip files (e.g. Windows Explorer or 7-Zip), a telnet client for debugging (e.g. Windows Telnet or PuTTY), and a way to connect to and deploy (side-load) your channel from your PC to your Roku (e.g. any web browser or cURL). Here's some more info on setting up a development environment on Windows without using Eclipse:
http://forums.roku.com/viewtopic.php?f=34&t=83613. If you can't connect from your PC to your Roku over a network connection, however, then you're out of luck. Depending on which Roku model you have, you can connect to a network using ethernet or WiFi. If your school doesn't want you connecting to their network but you have your own laptop, you may be able to set up an ad-hoc network (as described in the first part of this post:
http://forums.roku.com/viewtopic.php?p=491352&sid=50621e28714a0944eb9b1b5d9ca4a807#p492929), which can be used to connect to the Roku.