There is an open source version of vm-tools which is not supported by VMware.com so you may take your risk if you try it that way.
Useful information like official documentation from VMware is here: http://www.vmware.com/pdf/osp_install_guide.pdf
I found this useful as they tell you where to find the package and the public PGP key. Also an important module like vmware-open-vm-tools-kmod-source has to be compiled and installed inside the VM before actual installation of vmware-tools. Or else, part of the vm services will be broken legs and will not start.
Ubuntu has its discussion over this topic with some tips and instructions:
https://help.ubuntu.com/community/VMware/Tools
They mentioned about a new command called apt-add-repository which is not available in the version prior to 9.10, so you may need to get around this by other methods for installation. The preparation also involves un-installation of previous version of vmware tools and open-vm-tools as well.
Regarding apt-get PGP error, you may follow this link:
https://help.ubuntu.com/community/SecureApt
After all, you will need to reboot the VM and check its vmware-tools running status:
$ /etc/init.d/vmware-tools status
For verification of kernel modules, please issue the following command:
$ /sbin/lsmod
You might expect there should be something like vmxnet, vmblock and vmmemctl loaded after the reboot.
Hope this helps!
