1. open a cmd prompt and type ipconfig for each windows machine; in debian, open a terminal and type ifconfig eth0
all your addresses must be in the same range, & judging by what you've listed they prolly are.
ensure they all have the same netmask, such as 255.255.255.0 - which is fine for smaller networks.
2. the topology seems fine.
you could eliminate the switch if there are enough ports on the router.
3. on your xp machines, in network properties, tcp/ip properties, go to advanced, wins tab, "enable netbios over tcpip"
4. are there any other computers / printers on the network besides the 2 xp and the 1 debian? if so, do any of them get "duplicate network name" or something like that on the screen?
let us know.