Installing latest Ubuntu from USB pen drive, the 'try me' Ubuntu boots fine, but when I try to install there is very limited space. (just 1.5 MB ) but when I boot windows the Windows C drive says it has 90GB of free space.
You don't get this after selecting the option to install ubuntu along side windows in the previous step of the instalation?
If you do then you should just be able to drag the divider and choose the drive space
BTW have you defragmented the disk in windows before intalling Ubuntu? it's highly recommended.
Windows is reporting 'free space' not unpartitioned space. Ubuntu needs unpartitioned space. This likely means you need to repartition the drive so Ubuntu can be installed. Ubuntu normally offers to repartition the drive or you can do it inside Windows if you have Vista or higher.