I also faced a similar kind of problem while downloading Winrar from download.com. The dialog box would appear in every 10 secs and would interrupt, the message on the dialogue box was 'hee interval hee interval hee' that was annoying. It is actually an spyware. I could not browse certain sites like google and it also prvented me from downloading free antispyware.

You could run the anti spyware and delete those spywares.
If it does'nt work then you can download the tool called 'Hijack this'. Run 'Hijack this'  it will show the application and services running on your computer. You can then hijack the suspicious applications running on the system (do not hijack the useful applications). This could help you.

You can go ahead and clean the registry (do disk cleanup) after its done.

Good Luck