WUBI is a *very* crippled version of Ubuntu that from what I've heard Canonical is getting rid of. The problem with WUBI is that it is basically a rewritable Live CD image... nothing more. Try partitioning your drive by booting from the Ubuntu 10.10 Live CD. Ubuntu makes it very easy:
First of all, when you boot and start the installer, if you want any Flash, MP3 support, or other functionality you need to check both boxes after you hit "Next" for the first time. Then, click "Next" again. You will come to a list of radio buttons saying "Install side by side", "Erase entire disk", and "Configure partitions manually (advanced)". Click the first option. Then, you can just slide the boundary between the partition views back and forth to allocate space for Ubuntu, and then install and configure your time zone/user account.