Why wubi? Just get the live DVD of Ubuntu and then you can isntall it from there with a GUI. If you have some experience with partitions itüs very easy. Basically, you need a ext3 partition, set the mount-point to / (this is the system partition, I'd make it about 40-50 gb in size) and an other partition, set to swap, this is the same as the page file in windows and it should be about the size of your ram, but at least 1.5 GB.