Now that the buzz around is all about the lighter, faster, eye candy OS Windows 7 Release Candidate, you might have downlaoded the more than 2GB file of the OS.
But while installing, by default the Ultimate version of Windows 7 is installed which is not recommended for home users in case the system has lower specs. It is better trying the lower versions like Windows 7 Premium or Professional which will be much faster and lighter on a low end system.
1) Extract all contents of the ISO to a folder on the desktop, Mount it with VirtualCloneDrive or use 7-Zip to open the ISO up then copy all the files into the folder.
2) Browse into the folder where you extracted all the files to and open up the /sources/ folder and locate ei.cfg.
3) At this point, you have two options:
1. Delete: If you delete this file, it will give you options on which version you want to install during installation.
2. Edit: If you edit this file, you can set which version of Windows you want it to install automatically.
If you chose to EDIT the file, just open the ei.cfg file in notepad and edit:
Change the word to Ultimate or any other version you would like to install.
Preview of ei.cfg
Right now , Windows 7 Ultimate version keys are only available. So, in case you install any other version of Windows 7 using this method, see this post to use any verion of windows 7 permanently