You can convert the server to openSUSE 11.2 with Samba installed to share resources. Samba is the Linux duplicate of the windows SMB network sharing protocol. The xp client machines would not experience any significant differences when connecting to resources (printers, files, office docs, pdfs etc) on the server. Maybe your xp client machines use drive mapping to the xp server (like e.g. drive Z: ) to ghet at the files. Windows boxes map shared folders from Linux to drives like X: \ etc just as if it was a windows server.
You can experiment with servers by installing a Suse/Samba Local Master Browser in your Workgroup environment, to get used to the Linux software before converting the xp server.
There’s a stepped approach available for learning and implementing.