check inside, hope this can clear the issue up

1) control panel: uninstall all "search assistant" related programs.

2) go to "program files" folder, delete all folders related to the search assistant.

3) check registry table again for any key related to the "search assistant"

You may refer to this link for more info: http://www.scanspyware.net/info/SearchAssistant.htm

or google "remove search assistant", tons of solutions,

or try some spyware removal tools, search this forum,for the keyword "spyware",

or try hijackthis and killbox for advanced user.

Backup important files and recover the whole system, just in case your system is heavily infected.

Cheers