Program Files (x86) - what does this refer to?

The electricity went off last night and I'm having system problems ever since. I find I now have two sets of program files under the C drive and I don't remember that being the case before. One is labeled as (x86) and seems to have some older files, though it also has a yahoo folder the other one does not. Is it possible the system has recovered an older version? Am I safe to delete this? My system is slow and sluggish, yahoo toolbars has disappeared and I'm frustrated! Am using Vista and IE8. Thanks