Hmm, are you saying that you are doing the Boxer Rebellion for your Historical Investigation, or do you mean just as another Preliminary Case Study? I'm not too sure if you're able to do a topic that's on the case study list for Preliminary Modern History for your case study, but check with your teacher of course.
However, I do know there is quite a number of resources on this site.
http://www.boredofstudies.org/view.php?course=24 Just search for Boxer Rebellion and some resources should be selected, if not you can manually search through the list.
There are a few textbooks you could use also, the Preliminary Macquarie Study guides has an in-depth chapter on the Boxer Rebellion. Another really good textbooks was 'Retrospective Year 11 Modern History' as part of the Jacaranda publishing company, specific author is Maureen Anderson. This was a really thorough textbook, which I utilised for my studies of the case study last year during preliminary.
Unfortunately with Trials dwelling closer and closer I haven't got much spare time to help you greatly with your project. If you do struggle with something in particular do let me know, but I can't help with broad questions such as ones you've previously mentioned. There's a plethora of textbooks, so do check your school library and also you local library. Perhaps ask you teacher if they can recommend any other sources for you, generally teachers had a secret stash they can let you borrow for the completion of assignments.
Best of Luck. n_n