Heres my suggestion, Download either firefox or Google chrome... They are much better....
But that doesnt't answer your question.
to get ie back, you have to download it and install it like any other program. Use a flash drive and another computer if you have too.
http://ie8.msn.com/microsoft/internet-explorer-8/en-us/ie8.aspx
http://www.microsoft.com/windows/internet-explorer/worldwide-sites.aspx
One of those should work for you. If not, you can either try IE9 beta(which I highly reccomend if you want to stick to ie) or you can reinstall windows, or restore to a previous point.
And for the world wide sites link, Use the windows vista link.