Linux can use a print server program called cups and the smb protocol to allow windows PC's to print to it's printers. One can also print directly to cups from a windows box but that is for another how-to.
 This How-to assumes that you have cups printing setup and working properly on the linux box that the printer is hooked up to. It also assumes you have samba installed on the linux box and it can be browsed from the windows box.   In your smb.conf you will need to define a share for the printer. something like this. (example for an HP deskjet)

[hp940] printer = HP940
comment = deskjet 940c
printable = yes
public = yes
path = /var/spool/samba
use client driver = yes

The last line is critical or you will get "Access Denied" errors on XP.  Now add a new network printer in the XP printer control panel. Browse to the share and when it mentions that the server does not have a driver go ahead and install the right one in XP. At this point you will also need to edit 2 cups config  files  on the linux box to allow raw printing or the jobs will
vanish into thin air. :-) 

  In the file /etc/cups/mime.types: uncomment the following line. #application/octet-stream
And in /etc/cups/mime.convs: uncomment the following line. #application/octet-stream application/vnd.cups-raw 0
Now restart cups.
/etc/init.d/cupsd restart
restart samba
/etc/init.d/samba restart
and windows should now be able to print.
Happy Printing!