CUDA 7 Install failure

installing CUDA 7, installer says “This graphics driver could not find compat hardware, you may continue, but you will not be able to run CUDA applications”.

I have a 8800GT, i know it’s old, but i currently have CUDA 5.5 running on it just fine.
So is this saying, if i upgrade to CUDA 7, all the stuff i currently have will stop working?
or does it mean CUDA7 features will not work?

CUDA7 will not work with your 8800GT. 8800GT should be compute capability 1.1:

and support for compute capability 1.1 (i.e. sm_11) was dropped in CUDA 7:

"CUDA Toolkit and CUDA Driver Support for Tesla Architecture: The CUDA Toolkit and CUDA Driver no longer supports the sm_10, sm_11, sm_12, and sm_13 architectures. As a consequence, CU_TARGET_COMPUTE_1x enum values have been removed from the CUDA headers. "

The last version of CUDA that can be used with a cc 1.1 device is CUDA 6.5 (and its associated driver.)
You cannot use CUDA7 with a 8800GT and I would not recommend installing it with that GPU.

If/when you compile code for sm_11 with CUDA 6.5, you will receive a deprecation notice/warning. This was included to warn users that support for sm_11 would be dropped in a future release, i.e. CUDA 7.