Virus problem (kinda urgent)

This got onto my computer and I've no idea how it got there. I've used about 4-5 different virus and adware scanners, one of which took 12 hours it was so thorough, but nothing came up.
I've looked through the registry and scanned everything I downloaded the day it appeared but I can not find the root of the problem.
The icon thing itself is in the taskbar and flashes between a mine symbol, (not good), and a triangular warning symbol. Every now and then a bubble pops up headed 'Critical System Errors!'. If I right or left-click on either the icon or the bubble a window opens up to a website called 'virusbursters.com' which asks for login details or a credit card number. ...'nuff said.
Here's a pic of each little stage in its annoying but troubling regime of terror.
As you can see 'balloon' is spelt wrong which clearly indicates that this is not windows being retarded.
I kinda need to get rid of this. Can anyone help? Better antispyware/antivirus? Anthing?
Ross 'n Roll
I've looked through the registry and scanned everything I downloaded the day it appeared but I can not find the root of the problem.
The icon thing itself is in the taskbar and flashes between a mine symbol, (not good), and a triangular warning symbol. Every now and then a bubble pops up headed 'Critical System Errors!'. If I right or left-click on either the icon or the bubble a window opens up to a website called 'virusbursters.com' which asks for login details or a credit card number. ...'nuff said.
Here's a pic of each little stage in its annoying but troubling regime of terror.

As you can see 'balloon' is spelt wrong which clearly indicates that this is not windows being retarded.
I kinda need to get rid of this. Can anyone help? Better antispyware/antivirus? Anthing?
Ross 'n Roll