I can’t boot from a Windows 7 USB pen drive on my iMac begin 2008 (shortname IM81)

Verify Apple Computer Version on wikipedia http://en.wikipedia.org/wiki/Intel_iMac

If you have only 2 options in the boot camp assistant, or if bootcamp doesn’t recognize the windows installer disk when its on a bootable usb, it’s because bootcamp doesn’t recognize your MAC as a model that should install windows from a USB, its actually quite easy to fix, just follow these simple steps:

1. go to Applications>Utilities> right click on boot camp and click Show Package Conents, you’ll find a folder inside called Contents. Inside that folder exists a file called info.plist.

2. Right click on the folder containing the file > get info > change permissions so any user can read & write. Do the same for the file itself (right click > get info…).

3. Right click on info.plist and choose Open with > Text Edit.

4. at the end of the document theres a list of strings that contain different versions of Mac computers, the list is titled something like: “USB boot Versions”, add your Mac’s version to the string list ( MB40 ) if your version is Macbook 4,1 (you can see this by clicking on the System information App in the Utilities folder).

5. save the file and change back the permissions on the file and folder.

Now open boot camp and you should see the option to create a Windows 7 installler on a USB, and also bootcamp will look for a windows installation on any USB’s after you partition the hard drive.

That should get you past the bootcamp assistant phase, assuming your usb is indeed bootable, your mac should partition the disk and boot into the USB and start the installation (for some reason mine doesn’t recognize the USB as bootable but thats another issue)

FYI: Windows Official ISO’s http://www.mydigitallife.info/official-windows-7-sp1-iso-from-digital-river/