I'm using Ubuntu 10.04 64bit.
You can check whether you have installed Qt4 Assistant in "Ubuntu Software Center".
I don't think in Ubuntu 10.10 you can set the LD_LIBRARY_PATH. But you can add the library by doing
$ echo "/usr/local/Coin/lib" | sudo tee /etc/ld.so.conf.d/libcoin.conf
$ sudo ldconfig -v
I'm attaching the enviroment variable on my computer for your reference.
export QTDIR COINDIR PATH GRASPIT