having more than one anti-spyware utility does no harm.
There's a difference between anti-virus and anti-spyware. It is not wise to have more than one anti-virus running at the same time because anti-virus utilities check every bit of data coming into your computer, from the internet, or from emails, or CD/DVD's, etc for any data that exhibit virus like qualities, and so if more than one were running at the same time they would 'fight' for the right to check the data first. However, you can have more than one anti-virus and keep the other as an occasional manual checker. Personally I don't.
Anti-spyware is different. Like Rod I have more than one anti-spyware utility although I only have one running in the background continuously. But it does no harm to have more than one running. I use the others regularly for manual scans. Neither the anti-virus nor anti-spyware utilities have drivers because they are just software based and they do not run hardware.
Viruses are software that either do direct damage to your system or they drop other software that does other things, like spyware, trojans, etc. Spyware does what it says, they 'spy' on your computer usage. They can take many forms, and some are useful. For example, cookies can either be helpful or not. A cookie is a small text file that is installed on your computer by many web sites when you visit them. CNET drops cookies onto your system and these help you when you re-visit CNET. However some cookies spy on you to target you to display appropriate adverts on the web site, etc.
Other spyware is more serious. They can cause pop-up advert windows, or can spy on your passwords, credit card details or other personal details, and 'phone home'.
Registry cleaners are not anti-virus or anti-spyware and I would say that their usefulness is on the wane. With older Windows Operating Systems like Win 95, 98, ME they were handy to keep the registry mean and clean, because those systems tended to 'fall over' if the registry became corrupt. But newer OSs like XP and Vista are much more robust and can handle their registry's better. Registry Cleaners nowadays will only usefully clean out orphan registry entries, those entries that are not deleted when a program is uninstalled. but if a registry is badly damaged, by a virus, etc, then Registry Cleaners can do more damage than good. It is best to use backups, or to remove the damage with professional virus cleaners and/or specialists, as can be found when using specialist HiJackThis, (HJT), forum experts who will step users through which entries to delete/modify, etc. Registry Cleaners can be very dangerous to a user if he does not understand what he is clicking to remove, and I no longer use them on my XP machine except for a general purpose cleaner like CCleaner, which cleans out all my temp files and temporary internet files, and also looks for orphan registry entries.
Sorry, but the advice that anti-spyware uses drivers is wrong, drivers may be affected by spyware or viruses, but the anti-spyware and anti-virus utilities do not use drivers.
I hope that helps.