Ps3
I have a PS3, and I am also an IT Director, and I LOVE the PS3 for its flexibility in connectivity and uses. You do not have to have it directly wired for gaming... I had mine connected through wi-fi for over a year and could game online with CoD4 perfectly fine, no lag. As long as your PS3 can get decent signal strength from your wi-fi router, you will be fine. Most DSL and Cable providers are around what now? 6Mbps? (This is a very rough estimate, I know some places are up to 10 Mbps, but I feel that ~6 is a good average)Which is actually megabits, not megabytes, (one byte is 8 bits) that is actually .75 megabytes per second of PEAK throughput... on average you might be pulling .5 megabytes (~500 kilobytes per second or KBps) per second. The average 802.11g connection at full stength is 54Mbps, or 6.75 megabytes per second, so as you can see, even at half strength signal wise, you are still above the peak threshold for your broadband connection.
Secondly, yes you can stream music and videos from other computers on your network, but they do have to be networked together, which does require a router or a switch.
I would however recommend that if it is an option for you to do so, use the hard wired connection, is always more reliable and secure, but if it is not available to do so, then a wi-fi connection is more than enough to keep you gaming.