XP Pro to Windows 2003 migration

Mrss: one of my customers has a very small network with a PC with Win XP Pro acting as the server. For reason of growth and increase in application complexity he needs to install Win 2003 Server to replace the XP Pro. My question is:
Can we mount the the file system of the XP Pro in the 2003 Server ? or is there a way to convert the XP Pro file system for the Win 2003 Server ?
I will appreciate your help in this matter.
Cordially yours: Jose Solano