I heard something in the AV grp, but its WITHOUT Guarantee etc...
i don't know WHAT this changing, but i believe something with the packages size...

Right click on
My Network Places -> properties
Local Area Connection -> properties

then you see "connect using:" then you see your network card and right of this field "Configure..." click on it
then to "Advanced"

Then i think it was the "Flow Control", but i'm not sure whats happening and when your are not known what you're doing, better do not changing somethings.

here is the wikipedia link to the "flow control"
http://en.wikipedia.org/wiki/Flow_control