@MaydayDec 01.2008 — #If you mean, when someone visits the page it automatically becomes their homepage, whether they want it to be or not:
Not only would doing so just aggravate your visitors, as the above poster commented, but most modern virus protectors and even browsers block such an event from happening, and give a warning message that this was attempted.
I you think some visitors might have a valid reason for making your site their homepage, give them a link that allows them to do so, but do NOT try to force it upon them.
@felgallDec 01.2008 — #All browsers except Internet Explorer will ignore any attempt to change the browser home page from anywhere other than the browser preferences.
For Internet Explorer you should apply a registry update to lock that option yourself before some malicious web page updates your browser home page and then locks the registry to stop you changing it back.