Is it the Home XP or Pro XP? I'm not sure if this will make a difference - I know that in XP PRO you must go to the CD (extras? networks? well, it's in one of the folders...) and follow the install instructions for "netbeui" in order to share files with another windows system (including samba as well). Microsoft I believe is trying to lose netbeui and does not install this by default. TCP/IP installs right away though...
XP Home may install this by default - I have made it a point to stay from the crippled version so I cannot say for sure. Now before you flame me I like XP PRO. I also like OSX, linux (all flavors) amiga OS, unix..etc.
Also, the first batch of XP Home Editions were beta - so if you purchased your system with it installed already (even after the release date) make sure you have all the latest updates and patches. Usually, a popup displays with "there are critical updates etc."
Hope this helps