First up a move to IE6 is a must for security reasons alone.
Close all (browser) windows & rescan with hijackthis. When the scan is finished place a check in the box to the left of the following entries & click 'fix checked' :
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Bar = http://red.clientapps.yahoo.com/cus...rch/search.html
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = http://red.clientapps.yahoo.com/cus...//www.yahoo.com
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://red.clientapps.yahoo.com/cus...://my.yahoo.com
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Bar = http://red.clientapps.yahoo.com/cus...rch/search.html
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://red.clientapps.yahoo.com/cus...//www.yahoo.com
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://red.clientapps.yahoo.com/cus...://my.yahoo.com
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://red.clientapps.yahoo.com/cus...//www.yahoo.com
R1 - HKCU\Software\Microsoft\Internet Explorer\SearchURL,(Default) = http://red.clientapps.yahoo.com/cus...//www.yahoo.com
O16 - DPF: {56336BCB-3D8A-11D6-A00B-0050DA18DE71} (RdxIE Class) - http://207.188.7.150/0963c524256ebe...ip/RdxIE601.cab