Installing - partitioning failing

[Gary <listgj-deb@yahoo.co.uk>]

I have a system with a Windows 7 installation (NTFS) which I'd like to
keep and use "alongside" Debian. During the installation process I
reduced the size of the main partition which left a "hole" that the
installer labelled "unusable". I wasn't sure what to do with that, but
tried to use LVM to get it to use that as the place where it should
create a "group" (whatever that is).When I selected it and pressed

Return, the system complained. With a bunch of question marks. There
was no recognisable text at all. After that, the installer can't do
anything with the partitions - it fails to recognise them, I think,
and just springs back to the main menu when I try to select that
option again.

What have I done wrong? How do I fix it? Why is the installer giving
me sh1t? :-(