Base Photoshop version (4.0) won't lod on 64 bit computer

I first bought Photoshop 4.0 many years ago.  Upgraded to 6.0 and finally CS2.  I want to load Photoshop on my new computer but it won't accept the 4.0 full version.

What does Adobe offer its long term customers in this case?

Thanks

Kurt Schoelman