Is Internet Explorer 8 Safe To Download?

Hi, I Was Just Wondering Is It Safe To Download Internet Explorer 8? Or Should I Just Continue To Use Internet Explorer 7. Is There Any Problems With Explorer 8? I Also Have Firefox & When I Tries To Signin To A Certain Site It Lets Me Signin But The Ims Wont Work. But When I Use Internet Explorer 7 I Have No Problem. So Is There Anyway I Can Fix This? Thanks.