There are several different methods of transferring information from one 
computer to the next, each have their advantages and depend upon you or your tech's level of comfort with that method of transferring files.  The method suggested by WrapperX above is a pretty common option.  I've often always transferred files using either an external storage device like a flash drive, or transfer it through the network.  Instead of trying to copy over applications (which can sometimes cause errors working properly in the future) I've always installed all software fresh on the new 
computer using either the original CD or the downloaded setup files.
As for compatibility with your network, 
Windows 7 should work without any issues with the rest of your 
Windows XP computers.  There have been a couple issues occasionally mentioned when files stored on the 
Windows 7 
computer are shared to computers on the 
Windows XP systems, but not vice-versa.