I don't know about "good" popup blockers and firewalls. I know that you could use "zone alarm" as a firewall, and there are a number of others that a google search would come up with it. Windows XP Service Pack 2, Is supposed to come with a firewall also. Popup blockers is a whole different topic, because it could be based off of the page (the page you are visiting pops up the site) OR it could be due to adware and spyware on the system. Yahoo and MSN have "Internet Explorer Toolbars" that have these popup blockers for the browser, but I question their usability. You could take a look at using the web browser firefox (http://www.mozilla.org/products/firefox), which has a built in popup blocker.

If You are getting popups based on spyware / Adware, then you might need a tool to stop popups. You can take a look at Adaware, Hijack This, or Microsoft's Release (Bought from GIANT) of Anti-Spyware.

I Don't know if this helps, but I hope so.

My suggestions to my customers ....
Zone Alarm Firewall... Turn off the XP firewall.... (Never run both)
Spybot ... and update often
Ad-aware SE ... and update often
And I agree with the post above... Get and use Firefox....
You will not believe the difference...
If you dont mind spending a little money get the program to remove IE from XP
I use it to remove IE from 98 all the time.... Google 98lite....

This thread:
http://www.daniweb.com/techtalkforums/thread5690.html
Has a link to a free firewall which is better then the one that comes with XP.

It also has links to SpywareBlaster and SpywareGaurd, which will prevent many companies from putting the stuff on your computer that cause the pop-ups. Keep them updated!

As previously suggested, use run Ad-Aware SE and Spybot regularly to catch things that get past your protection (yes, it will happen).

An alternative browser, such as Firefox or Opera, are recommended because they are less prone to unwanted intrusions. You need to keep Internet Explorer, however, as this is the only browser that you can get your Windows Updates with. Keeping Windows and IE updated will also help prevent pop-ups.