open gl makes me disconnect from server in cs

Every time I play cs or any hl mod with open gl graphs my net connection is disconnected and reconnected during lvl changes. That causes me to be back on my desktop with res. 640x400 or smth.
My connectio dsl 512/256
graph is nvidia geforce2 mx/mx 400
msi motherboard k7a/t with 1 ghz processor
ram 756mb
win 98
latest drivers been installed for graph card