toolbars often do this - their installer are often incomplete
The "Ask" toolbar is "legit", but even so can still cause stability problems
If you can't get rid of a program like that easily, another way is to disable it using Autoruns
Autoruns for Windows
If I'm cleaning a machine up, Autoruns is one of the first tools I use, simply to stop things running, enabling later removal of them
But its a dangerous program if you don't know what to delete
A similar good program - though not much use in Windows 7, is Trend Micro's "Hijack This"