I had this problem for a very long time and did everything everybody suggested here and other websites. Talk about banging your head against the wall. I finally decided to try and tackle it one more time(probably wouldnt have been the last time)
It had nothing to do with firewalls or windows not able to see the PS3 it had everything to do with the router itself. I have a Netgear WNR2000 router I decided to update it and check the settings What I found was the "Enable Wireless Isolation" box was enabled and what happens is: (copy and pasted from http://www.routerlogin.net)
If checked, the wireless client under this SSID can only access internet and it can’t access other wireless clients even under the same SSID, Ethernet clients or this device. Other clients can’t access the wireless client, either.
After unchecking that silly little box, my ps3 was finally able to find the media server. Talk about jumping for joy. For those that have this similar problem you might want to see if your router has this function. I sincerely hope nobody ever has to go through my same headaches and I hope this works for you as well.