Linux DBMS to share with Win

[Matt Neimeyer]

I'm using Samba to allow my users to store their database on a Redhat 6.1 
file server.

I've got some who want to shift to using Linux instead of Windows but the 
DBMS they use is not supported (yet... I'm told) on Linux and I'm afraid 
that multi-user access on different OS's are going to screw things all to 
high heck anyways...

But that being said...

Are there existing DBMS's out there that can co-exist on Windows and Linux 
using Samba as the link between both worlds? So that all clients can share 
the data?

Any advice? And if this isn't the right place to ask is there anywhere that 
is better? I was guessing Samba was the place to start since that's how 
"both worlds" talk...

Matt