I'm sorry to say, Avast 5 is still not satisfactory.
I was helping a friend with a suspected infection on her Vista laptop. We downloaded avast 5 and attempted to install. Two problems :
1. Despite being a new install, there wasn't an option to do a boot-time scan, like avast 4.8 does, to "nip those nasties in the bud".
2. More importantly, the installation BLUE SCREENS and after reboot, says something like "avast is in an inconsistent state" and is unable to function!
So after two attempts at installing avast 5, we installed an old backup of the avast 4.8 installation package (couldn't find it here anymore). THIS installed successfully and did offer and perform a boot-time scan.
Since by this time, it was almost 2AM, I left to get some sleep, and am going back tomorrow to install more recent virus definitions for avast 4.8 and re-scan the lot (as the installation package built-in definitions are way out of date, of course).
So, as you can see, avast 4.8 is still needed even for Vista, let alone for W98!
Joe.