Windows Vista, Firefox 5.0 (though it happens on IE as well)

Occasionally my cursor will freeze and I'll hear a "beep"...after a few seconds the cursor goes back to normal, and I get a pop-up that says I have a script that is busy or has stopped working. The pop up gives me a choice to wait for it to start working or stop. I always choose wait, if that makes any difference. The script in question (and I have no idea what a script is, so maybe you can enlighten me on that too) shows a ford-trucks.com URL and a 12 character code, followed by "avg_ls_dom.js:396". My ever-so-limited knowledge tells me that this probably has something to do with my bloated, over priced, resource-hogging anti-virus package but I've got absolutely no idea if it can be corrected on my end.

Any and all ideas/suggestions are welcome, but I'll warn you that attempting to talk me through a potential fix might try your patience