If the xBox supports a standard FTP, then it shouldn't matter what platform you use. Also everything that I have done network related on Virtual PC has worked great, so if the Mac is a problem, VPC works well. (Like programs that find unconfigured HP jet directs, or routers, work great for me in VPC.)
The ftp command in terminal does all I need, but I am an old PC then UNIX user. 😀 I am sure there are some good graphical FTP clients for Mac.