there are a number of ways to do this you can add a bit of code that checks the users ip address and if it is the one you want rid of then redirect them elsewhere.
if you have a script to prevent the ip address getting in but as you saw it is on a network so the start number be 123.456.78. but the end numbers vary from .34 to .67 and so on so rather than listing every number simply put th ip address like this 123.456.78.* this way any ip address with these numbers at the strat are denined access.
it can be something as simple as this
if Request.ServerVariable("REMOTE_ADDR") = "123.456.78.*" then Responce.Redirect(http://www.paintdrying.co.uk
") End If %>
this bit of code will check if the person viewing the page is at an ip address if it starts with 123.456.78. then the person viewing the page will be autoredirected to www.paintdrying.com.
this can be cahnged to suit and ip range and depending how cruel you are any other website.
Hope this helps you out. if you ad this bit of code on a file and save it.
then run a bit of code like this on the very top of each of your pages in your site:
it will mean that you only ever have to do it once then after that if you want to block other people accessing your site you simply change the ip_redirect_script.txt and it will automatically block access any page with the include fiel tag on the top of it.
i hope this is help fully