I am a registered user and I use Windows Vista Home Premium 32 bit
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A registered user will only be able to install from the original email link, CD (in some cases), via Impulse or possibly SDC. Since you are using version 6.4 I would normally suggest Impulse........ but since you've got issues try SDC. Understand that if you've installed any of those other versions (Download.com, Freeware Files, Major Geeks) you've got to get them totally uninstalled before using either SDC or Impulse.....they are the trial version and the trial cannot be "updated" to full version.
Just so you know.....If you get it installed and running you can then uninstall Impulse afterward.
I understand some people have issues with Impulse but I (like the vast majority) have not had any problems with it. I always use the betas, currently installed on my office desktop (XP Pro) my laptop (Vista Home premium 32 bit) my home desktop (Dual boot Win 7 RC & Vista Ultimate 64 bit)