Linux - WinXp network problem

Hi all,
I have quite unusual problem with my home network and i hope there is
someone who knows the solution.
there are 3 networked computers
I run dual boot machine with winxp and slackware 9.1 linux, NIC is via-rhine
running on default kernel driver, i think that version is 1.10,
i have few services running like proftpd, httpd, samba, and they are
accessible from the internet thanks to noip software.
the problem is that im connected to the internet using internet connection
sharing on winXP machine. when i use winxp on my comp everything works fine,
but when i want to use linux (that would be probably most of the time)
everything works fine for a while, sometimes its 3 hours sometimes 3
minutes, and then windows machine 'forgets' about my linux box. from that
moment there is nothing i can do, i can't ping to that computer because it
looks like its switched off. when i reboot it won't help, i can't see
connection even in windows (network cable disconnected). the only thing that
helps is disabling and enabling network connection on winXP machine sharing
the internet. problem is that i have very limited access to that machine and
it's real pain sometimes when i cant use internet for the rest of the day,
just because i wanted to use linux for a while.
i think i didnt have that problem before i upgraded slackware from 9.0 to
9.1,
NICs in winxp are some kind of realtec cards, one of them built into the
motherboard, but the problem is with both of them.
i've found something about command: 'net server config \autodisconnect' in
win nt/2000/xp but changing its value didn't help at all. power saving
settings are switched off as well.
I've no clues whats going on. if you know the answers, or have any ideas
where to find them please let me know.

ps. please forgive my english, as it's my second language.