Greeting's

best software to stop a spyware from infecting your computer are

1. Firefox (browser) (best way to beat spyware as of now)
2. Get microsoft antispyware beta (has real time protection)
3. A nice anti-virus protection (don't forget to update it, I mean tell your customer's that) <--- even some anti-virus vendor's have added spyware scanning and cleaning to their anti-virus software but this is not as good as an anti-spyware programe.
4. A nice firewall (Sygate, zonealarm and outpost pick your choice) &lt;-- only for security not much for spyware problem.
5. Get either spybot or ad-aware any on of them as backup for spyware removal.

last but most important UPDATE WINDOWS. &lt;--- very IMPORTANT STAGE.

over this if you want little extra protection,

ask your customer's to surf the internet using a LIMITED RIGHTS ACCOUNT and not administrator account and always to delete temp file's after they are done surfing.
a good programe here is www.ccleaner.com

also to change their internet security setting's to high and tell them to turn ON download if they have changed their setting's to high.

Hope this help's