1st thing is to clarify the languages/technologies used. 1st you mention an event timer. and being the c# forum we would naturally assume you are talking about 1 of the timer objects in the .net framework.
then you mention ajax, which is a different environment, language.. well a different context all together.
so, assuming now a web context, .net timers are out. as the .net code is server side. so you timer would be on the client. which means javascript. as you mentioned a user can disable javascript. there is no way around that. 2 options around this are:
1. have the user experience degrade quietly to non-ajax behavior if js is disabled.
2. have the browser test for the availability of js. if it's not there (disabled) display a message to the user stating the user must enable js to view the website. for more help with either of these options I would use forum216 and forum215.
I would also highly recommend using a js library (jquery, mootools, protype or dojo) for your client scripting. otherwise you have to write alot of plumbing/infrastructure code to handle browser variations.
as for your other questions above preventing the user from overriding timer control. This may be better addressed after addressing the js issue and explaining the context using the appropriate language.
Jason Meckley
Programmer
Specialty Bakers, Inc.
faq855-7190