Yes, it's very easy to do with Windows Media Player.
Open Windows Media Player, and click on the bottom section of the Rip button, which will open a drop-down menu. Click on More Options, which will open the Options applet. Click on the Rip Music tab, and then open the Rip Settings format drop-down list. It'll be set to Windows Media Audio (.wma) by default; simply change it to mp3, then click apply and OK. Close the Media Player.
The next time you open the player and rip a CD, it should automatically save it as a mp3.