R. Arjona,
WIN7 is definitely better at networking than XP. I have mostly WIN7 64-bit and a few scattered XP Pros and, if anything, the WIN7s are faster. Of course, it depends on your setup.
My bet would be that XP Pro in a peer-to-peer has a 10 connection limit. This INCLUDES networked printers and scanners. It's a little weird, because it is usually all or nothing.
To test it take three clients off the network. Reboot all the other computers so there is an election (may not need to do this but just to be sure they all are given a connection).
If this works and your laptop is as fast as the others, change your "server" to a WIN7 machine, which can handle 20 simultaneous connections. Otherwise, go with a server OS, which can pretty much handle as many as you throw at it with the exception of SBS which is 75.
