An Airport Extreme base station (AEBS) will agregate AFP and SMB shares for your connected media devices over USB, you can even hook up multiple drives provided you use a powered hub. You just have to be a little cautious with your file names as Windows machines won't load certain files due to the use of invalid characters e.g. having colons : in file names, or having a file name that is over 24 characters in length.
I run a 1.5TB hard drive connected to my 4th generation AEBS to aggregate shares on my network and to manage everything. you can set up the file permissions you like also by just using the disk section in the Airport utility. It works quickly, easily and simply, and if you just need a couple of shares set up on your network I really can't fault an AEBS for this, even if there are many things I can fault an AEBS for.
The Disk attached to my AEBS contains the iTunes Media folder for all of my iTunes libraries and also all of the files for my time machine backups. The only time it ever fails is when I have to reboot my main router that controls DHCP handouts and iTunes is open at the same time, other than that its faultless and has less overheads than a dedicated server.
I ran a G5 Xserve for a time as a dedicated file server but it was too noisy, hot and inneficient to just have it there for show which is just about the only reason I had it there in the first place apart from having it running as a transmission daemon.
