Crappy networking and firewall issues

Hey guys,

I was trying to play a little bit with my Leopard loaded MB's and I decided to understand how the Screen Sharing and networking stuff worked and I found that was a little before impossible to make this thing work. Trying to connect to another Mac on the network seems to be not possible, since the firewall is blocking all the incoming packets, even though File Sharing is active and allowed to go through the firewall... When the firewall is off, it takes a long, long, long time to load and it usually rejects the password (double and triple checking is the correct one, of course.) Screen sharing doesn't seem to be responding in my compy. It tell me to input an username and password (when it loads, about 6 out of 10 times) and none of the admin passwords or usernames seem to work; they all get rejected.

iTunes streaming doesn't seem to work either. It takes for ever to load the other's computer library and it never finishes loading the song/video.

I've been renting a couple of movies from iTunes Store and I like it... but I realized that Front Row isn't compatible with movie rentals. Is there and update I'm missing?

Thanks guys for your time... I'm not ranting or complaining. I just want to know if someone else has had a little bit more success with these same things. Any suggestions?