Right, for now you should ignore hardware/software/hosting issues and work out what you actually want the intranet system to do. Do you want it to help workflow, track projects, track customers etc...
Once you have a clear idea of what purpose it needs to perform, have a look and see if there's any software out there which is fit for purpose. If not, you'll need to develop your own. This is when you need to speak to someone who knows how to develop an intranet system really, don't ask on a forum or you'll get replies like the one above
One thing I'd really reccomend though is not trying to cut corners while building the intranet system. These things have a habbit of growing in to big systems which the whole company relies on. You really don't want that sort of thing cobbled together by someone inexperienced as it'll only get harder to maintain and add new features to. You certainly don't want it running on some old computer you were using as a foot rest either