Cannot do a System Restore

Hello,
This morning on my PC (WINDOWS XP Home edition) a
malicious script was installed, you know the ones that
annoyingly reset ur homepage and no matter how much you
apply your preferred home page, the next time u start
Internet explorer, the malicious one is loaded.

Well that can usually be taken care of by doing a System
Restore, but it won't let me, it doesnt do it properly,
just comes back with message 'restore Incomplete'.

What can I do?

Thank You,
Jay