usb stick virus

I just finished ordering a fresh cd of windows 7 home premium + download. I plan to burn it on a usb drive and do a clean install. The reason is because I suspect my system was infected by a virus(I was redireceted to a filestube page with rar password download)even though I have comodo firewall + defense installed and do regular virus checks with trend micro free scan and microsoft security essentials tool, and none of these show any virus found.

So if I burn the iso file on the usb stick then install it, would this be secure enough since I heard some rootkits install themselves on usb sticks and that is how they infect and spread themselves onto other pcs. I have scanned the usb flash drive with microsoft security essentials and nothing was found. Can anyone confirm if this is enough or should I wait for the CD to arrive and then do a clean install?

No USB is safe. You can get it infected whenever you insert it in a running system infested with nasty viruses. The best thing to do is to plug it in before the operating system starts, boot from it to start installation and don't use it everywhere. Once you have downloaded it to your USB, you cannot use it for transferring files, etc., just for Windows installation.

I am burning the iso file from the same drive that the virus have been installed on.

I scanned with mcafee antivirus, comodo antivirus before burning the iso on it apart from formatting it as well. I don't know if that takes care of it surfficiently or not.

Also is it more secure to install it fro usb or just mount the iso with an iso mounting tool and then do a clean install?

It is my understanding that Flash Disinfector is only compatible with Windows XP 32-bit and sUBs is not planning on updating it. Panda USB Vaccine is another option, as is dr_Bora's MCShield::Anti-Malware Tool::.