You've got Spyware! Probably of the type that loads along with IE and monitors what sites you surf, reports back to the mothership when you land on a page that relates to what they advertise, and then makes IE open up a web popup. The site you're surfing, in this case EpicSki, has absolutely nothing to do with it.
Unfortunately a federal court<a href="http://yro.slashdot.org/article.pl?sid=03/09/09/0325225&mode=thread&tid=111&tid=123&tid=126&tid=99
just ruled</a> that this is not a violation of the host site's copyright.
It gets on your PC from things like Kazaa or Bearshare or other P2P sharing programs, downloads of "browser helpers" and other "add-ons", clicking on those dumb "your Internet Connection may not be optimized" ads, and if you use Internet Explorer instead of a modern secure browser, sometimes just by surfing to a site or by opening an email that enables IE's "drive-by download" feature (actually ActiveX downloads)
If you use Internet Explorer, you're much more subject to all kinds of "mal-ware" including "drive-by downloads". Both because of the "software monoculture" of almost all MSIE so that's what's targeted, and the inherently insecure nature of Internet Explorer. Use Mozilla (or a mozilla-based browser: Netscape 7.2, Mozilla Firebird, etc.) and you're immune to most of that and get a better browser.
You maybe have to use IE for the 1% of brain-damaged sites that don't work right due to bad, non-standard coding, but it shouldn't be your everyday browser if you want to surf safe.
Seriously, if you use Mozilla (or Netscape 7) for both browser and email instead of MSIE and MS Outlook Express, you'll be immune from practically any web/email-based attack vectors. You still need anti-spyware software though
Regardless of what you use, nowadays you need "anti-spyware" programs just like anti-virus, in case ad-delivery or privacy-invasive software lands on your PC from other downloads or installations. Ad-Aware is free and very effective, and relatively user-friendly.
Never install any of those "browser buddy" or "Gator" or anything like that - they don't do anything meaningful but by installing them you've "agreed" in the fine print to allow ad-delivery software and spyware to be downloaded onto your machine without further notice.
Very good overview and recommendations in this PC Magazine article
except they don't seriously mention alternatives to Microsoft Internet Explorer, because that would be offending their major advertiser. Otherwise a good resource.