Your computer probably has malware. Run ComboFix and that should fix the issue.
http://www.bleepingcomputer.com/combofix/how-to-use-combofix
http://www.bleepingcomputer.com/combofix/how-to-use-combofix
Edit: There's no choice of browsers on this network. It's IE 7 or nothing.
http://sitecheck.sucuri.net/results/http://youthoughtwewould...