Will SP4 install on W2K undo previous security patches

yes, you will be required to install security patches with SP4. Though SP4 will cover all security patches released before SP4. I'm not too sure about whehter it will have to reinstall post-released SP4 installed before you did SP4, but it's something of a null issue, given that there are secuirty patches for SP4 itself and that you haven't installed already (5 out today) kind of make this a null issue. There is a way to load all the fixes onto a CD and then install them that way, which would greatly increase the speed with which you download the patches and whatnot. I would suggest looking into that. Or if you have a server available, you can setup a mirror type thing of the windows update site and use the server and push the updates to the clients from there.