This tool was probably installed during installation of other wanted software as additional recommended software (but still must be possible to reject it).
I would recommend to reset Internet Explorer settings and disable all unneeded add-ons (related with MyStart tool).
In case the situation still persists, please gather Gmer anti-rootkit and Autoruns outputs, upload it in an archive (zip file) to favorite online storage and provide us with link to it, so we can analyze the situation.
Comments on the web suggest My Start by Incredibare is Malware which hijacks whatever browser I use. I have uninstalled it using Control Panel - but it still hijacks IE. Can AVG get rid of it?
I am using Windows XP.