Network TCP/IP Problems!

Please take the time to read this message, it means alot
to me and if you can help me i will be more than grateful.
I have a Home network. The Host ocmputer of the network
connects to Comcast Cable modem high speed internet. On
both client computer, lately, there have been some
problems. Usually in the beginning of the day they
internet will work great on the host computer and the
client computers, with speeds of 1500 kb/s each.
Although we currently do not have any firewall programs,
the LAN acts as if it does. If a client computer makes
too many connections via the internet, the host computer
will emmediately stop sharing its internet with that
computer, and very often both computers! Examples of
when this happens (all actions on client computers) : I
send files via MSN messanger, download from too many
people with kazaa or from a website, refresh the server
list for halflife, and occassionally while playing
warcraft 3 on battlenet. i know for a fact doing these
things causes the problem. for instance, with kazaa, if i
download from too many different users at one time, the
internet can not work again until i disconnect from
kazaa. Once that is complete, i can disable, and the re-
enable the connection. But after this, if i turn kazaa on
again, without downloading ANYTHING, the internet
automatically shuts off emmidiately. During the time
that a client computer has no internet, it has NO access
to the network, which means the other client computer,
and the host. Wether the host computer is logged in or
not does not change anything, so this rules out any
firewall software, trojans, or viruses. Also the client
computers are not running anything like this either, as
the problem still occurs when the only programs running
in task manager that is not under the SYSTEM category is
called EXPLORER, and whatever 1 other program i am using
(msn messanger, kazaa, ect...). I am also certain that
this has nothing to do with comcast, as i have already
contacted them. The only thing i could think of is maybe
in an Automatic Windows Update there was some sort of
firewall protection. But i do not think this is likely,
nor do i know where to find information on this. If
anyone can help me at all please post! i can use all the
help u can think of even if ur not sure its correct.
Maybe all u have is a simple suggestion or a "maybe its
this". I hope i didnt leave out any needed information,
or spam u with annoying unwanted information. Thank you
for taking the time to read this.