Parts of it sounds like you have ad support software installed. These programs are bundled with free software that anyone can download on the net. They can do things like change your home page which is ussually done by the like of lycos search bar or by another ad-ware. Your system will also slow down since it is sending usage data to the originator of the program which will in time send pop-up's ( the faster the internet connection the faster the pop-up's).
If you still this this is a virus then it's time to stop using the standard AV software like Nortons and try PC-Cillin by TrendMicro (www.trendmicro.com) You can also do a free online scan of the systems by selecting the personal tab and then click on house call. TrendMicro offers different levels of software so that even the biggest corp can be properly protected. It's the only AV program that I use and I can proudly state that nothing gets through without being scanned.