What kernel headers did you have installed before? The correct kernel headers are installed by default for all Ubuntu architectures, to prevent exactly this. Also, nvidia-current has a dependency on "linux-headers-generic | linux-headers", so it should either pull -generic if you did not have any installed, or use an existing one if you have another flavour (like linux-headers-server).
What kernel headers did you have installed before? The correct kernel headers are installed by default for all Ubuntu architectures, to prevent exactly this. Also, nvidia-current has a dependency on "linux- headers- generic | linux-headers", so it should either pull -generic if you did not have any installed, or use an existing one if you have another flavour (like linux-headers- server) .