touch&go,
A thought for your sister. If she needs the Google Toolbar for searching the web, since she does it so frequently, then ok. Now if she uses it because she gets so many popups, then I think she should consider going without it.
The problem I find with popup stoppers is, they mask a problem the computer is having and you do not find out about it till much later than you should.
If you do not have a router or some other form of Firewall, I would disable the Messenger Service as mentioned in the Guide I linked earlier.
To Stop the Messenger Service:
Start >> Control Panel >> Administrative Tools >> Services
Then Find Messenger and change Startup Type from Automatic to Manual.
Take Care,
Richard