Turn PC into a DLNA server

Get Windows media player 11.

go to Tools - options - library tab - configure sharing - check the box - allow unkown device - ok - monitor folders (here you select folders to be shared and enable sharing of folders in the list). Now search and your DLNA devices (eg PS3) will show up.

A better solution is to use serviio. It is free and you can configure which folders are to be shared. Twonky is also good (paid application), but I think it's memory footprint is higher than serviio.