Computer loses file sharing ability if booted out of sequence

I began noticing some network connectivity idiosyncrasies when
connecting my laptop to my network. My objective involves syncing my
desktop with my laptop after work. My network router and file sharing
facilitate this aim, yet fail whenever one plugs the laptop after the
desktop boots; or starts up the laptop before the desktop. Another
problem occurs when I unplug the laptop Ethernet cable and plug the
cable a few minutes later. The computers see each other, yet can not
share files. My workaround involves powering all machines on the
network down restarting the desktop; then the laptop; and then the
other computers. My computers are running Windows XP Pro with file
sharing on and connect through a Linksys router. My theory about these
idiosyncrasies points to how the DHCP assigns each computer an IP
address. But I have a vague idea on resolving this situation on the
fly. Let me know if you have any ideas for manually resetting the
network cache/DHCP/IP from the command line or Windows XP (without
powering down). These methods should help me access file sharing
resources when I connect to shared drives on my corporate network or
my home network as well.