Can’t remove spyware dialer

Dear all.

A user of our network (Windows 98) opened a spam message and his PC was infected by a dialer.

I scanned the PC with ad aware and spy bot but the problem remains. This malware wrote something to the registry and I can not get rid of it because every time the PCs boots it runs in start up.

Although in start up folder of Windows 98 I can not see something I suspect that this is a registry issue.

Any ideas where to look in the registry in order to remove this malware?

Thank you in advance.