need to install new service pack to re-install Quickset?

I just had a trojan horse removed from my Vostro 1400 laptop by a professional. Now I have noticed that the on-screen volume indicator that used to appear when I use the keyboard volume controls does not appear.  The same with the screen birghtness indicator.  Somewhere online I read that I need to reinstall Dell Quickset.  I have downloaded it, but when I click on to install it I get this message: "This installation package cannot be installed by the Windows Installer service. You must install a new Windows service pack that contains a new version of the Windows Installer service."   My computer came with XP Service Pack 2.   What service pack do I need and where do I find it?