This question already has an answer here:
So I hava a TOSHIBA laptop (64 bit) with Windows 7 Home Premium. First I downloaded wubi.exe and I installed it to my laptop. The only problem with this when I start Ubuntu I always get an error: Prefix is not set.The ubuntu boot up succesfully after 1 minute but it is very slow. So I want to reinstall ubuntu from a CD. I burnt a Windows 7 Home Premium (english version) iso for a Verbatim DVD-R and an Ubuntu 12.04 (desktop edition) (amd64) iso for a Sony CD-R. Okay I'm a beginner. Please anyone write me the method step by step: how to dual boot Windows 7 with ubuntu 12.04 I have the Installation disks, what is the step 2?