They can, just not fully up to spec. Even my P3 667 with a 32MB geforce2 downstairs can run spring at 800x600 with most effects off, but the main crippling aspect is the lack of map shading, which makes it impossible to read terrain heights visibly in the overhead view. The game otherwise doesn't run that badly though...
I used to run Spring fine with that card. I could go grab it and throw it back in my computer to test it if you like. But it used to run fine, just not with shadows or anything.