Before you go over to the XP side of the forum let's do some minor HJT fixes first.
Scan with HJT again and put a check next to these items, making sure all browser windows are closed includeing this one so print this or create a new text document on desktop by right clicking an open area select new text document and save it to what ever you like. Now put a check next to these:
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://red.clientapps.yahoo.com/cus...//www.yahoo.com
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Bar = http://red.clientapps.yahoo.com/cus.../search/ie.html
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = 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
O2 - BHO: Yahoo! Companion BHO - {02478D38-C3F9-4efb-9B51-7695ECA05670} - (no file)
O4 - HKLM\..\Run: [AlcxMonitor] ALCXMNTR.EXE
O16 - DPF: {C02226EB-A5D7-4B1F-BD7E-635E46C2288D} -
Again make sure all browser windows are closed and click
FIX
Now reboot into safe mode by
tapping your F8 key upon restart and safe mode screen appears, select safe mode and press enter.
Go to Start > Run and type:
CLEANMGR.EXE and hit enter.
When prompted select the C: drive and click ok.
Check the boxes for:
Temporary Internet Files
Downloaded Program Files
Recycle Bin
Temporary Files
Click OK or Enter
Reboot and go on over to the XP forum.