This is a known problem when trying to compile the current vmware modules against 9.10's kernel
Follow the instructions here http://www.ubuntugeek.com/how-to-install-vmware-server-2-0-x-in-ubuntu-9-10-...
Also you will run into mouse focus issues with the vmware console plugin and firefox 3.5.6, Personally I just launch the console directly, there are instructions on how to do this in the comments on that article.
It's worth mentioning that unless (like me) you need a particular feature provided by VMware and not by virtualbox you might want to consider using that instead.