SEGA has released four classic games from Dreamcast on PC via Steam, three of them being re-releases.

Here goes the list:

-Crazy Taxi
-Sonic Adventure DX
-SEGA Bass Fishing
-Space Channel 5: Part 2

After doing some research on the Internet, I found that Sonic Adventure is a port from the XBLA/PS3 version (with the blue borders) which was a port from the original PC version. If you're thinking of buying the Steam version, better think twice!

EDIT: I found out that there is also a retail version (for stores).