[syslinux] iSCSI booting Windows XP

[yunch3]

Dear Developer:
    i am working a project including iSCSI booting.  i have a iscsi server with windows xp system image and fedora system image, and a booting server providing dhcp and tftp services.I made some menus using pxelinux and things are working fine with linux, but failed with windows .
    i use the following strings in my dhcpd.conf:
    .......
    filename = "pxelinux.0";
    option root-path "iscsi:192.168.1.222::::iqn.2001-04.com.example:storage.disk1.xp";
    .......
   and in the tftp booting directory i have in  "pxelinux.cfg/default" :
   ........
   label linux
   kernel vmlinux
   initrd initrd.img
   label xp
   kernel gpxe.lkrn
   ........
   the problem is every time pxelinux have downloaded gpxe.lkrn ,it try to "Booting from filename "" from tftp://0.0.0.0/",it seems that the "option root-path" parameter have not passed to "gpxe.lkrn" .
   it is said that when the "filename" option is "" in dhcpd.conf , pxe turn to "root-path",i have tried so ,however net-booting stop at "no boot filename received".
   i am sure there is no problem with my iscsi server,because i can boot xp by hand input "sanboot iscsi:192.168.1.222::::iqn.2001-04.com.example:storage.disk1.xp".
   By the way my NIC type is RTL8139/810x.
   i'd like to know the right way to congfig  my boot server to boot xp directly throught gpxe.
   Thanks in advance, Tomaz Kavcic (Slovenia).