The newest Company of Heroes patch, 1.70 now adds Direct X10 support.
http://www.nzone.com/object/nzone_coh_downloads.html
The DirectX® 10 Patch (version 1.70) has finally arrived and will breath new life into Company of Heroes. New features include: soft particles, CSAA support, instanced foliage and ambient objects, short grass using instanced terrain shells, and normal map compression.
http://www.nzone.com/object/nzone_coh_downloads.html