Browers: gotta use one these days, or you can't read your favorite blogs and news sites, buy from Amazon, or easily order opera tickets from a company on the other side of the country.
Internet Explorer still has a large market share, despite the presence of several faster, better-designed browsers. Lots of people are still using it, because it's installed on every Windows computer (and probably Windows is configured with IE as the default browser). It's just easier to use what's there than to find and install one of IE's competitors.
IF you are using IE, check the version. If you're on IE 6 or 7, upgrade to IE 8 or 9. Seriously. The more recent IE versions have technical improvements that are not available on old or patched versions, mostly in security areas. Moreover, Microsoft itself no longer supports IE6.
If you're switching browsers, Firefox, Chrome, Safari (which does, indeed, exist for Windows), and Opera are all faster than recent IE versions. (Opera is supposed to be the fastest of all, but OH GOD the interface is horrible.) They run just fine on older computers - which I know because I use both Firefox and Chrome on a Dell I purchased in 2003. Windows XP, half gig of RAM only, slow processor.