Avira antivirus

hi,

I m tring to install avira antivirus personal on windows xp with sp2 and not able to install it. I tried with firefox first and after downloading the file which is shown by download status as completed but not able to run after so many times even after restarting the pc.And if I try with ie 8 after downloading that file with 29mb and try to run that file I get error "windows has detected a serious problem with this file".I don't have any antivirus or antispyware.Previously I had malwarebytes and superantispyware which I removed successfully from add/remove programs and also deleted some manual entries from registry,progrms files,documents and settings etc but not getting any sucess so plz help me through this