Slimserver runs very well on Linux. I used it for quite a while before eventually switching to a Mac mini.
The biggest problem you're likely to face is getting Windows to see your Samba shares from the Linux system. In my opinion, it's not a problem with Linux, it's Windows networking that's broken. An alternative would be to download "Windows Services for Unix" and use NFS instead of SMB. Of course, the Windows NFS client isn't all that great either...
-Rob