> Or
command 2>&1 | tee error.log in case you want th see the output while it is running. -- hendrik
If this doesn't work for you for whatever reason, you can use gpm instead (apt-get install gpm) which gives you mouse copy and paste on the text console. Also note that there is usually/var/log/XFree86.0.log and sometimes ~/.xsession-errors which give you details.
Regards, Pailus