networking issues via a hub (setting up an Fserv)

hi i currently run an 8Mb ADSL connection through a router with only one ethernet port out this is then split via a cheap hub to three computers. this ssetup works fine and all computers can access the internet at any time regardless of each other. i have spent a while trying to get the network up and running so that each computer has a static ip and is sharing required files through the workgroup (all running win xp pro); all well and good so far,

my problem now comes when trying to setup a fserv on Mirc i have forwarded the required port (59) to the computer that it will be running on and it can connect to and download files from other users w/o an issue the problem comes when i try to let others have access to my files. they can access my computer and browse my files (ones i have made availible) but the second that they try to download it my computer disconnects from the internet and i have to reset in order to get things running again (at this point im not sure whether or not all computers disconnect or just the one). now is this an issue caused by the hub (half duplex?) i have recently put an order in for a switch (full duplex) will this solve my problem or should it work ok in this setup (i.e the router is the problem)

router model Bt voyager 205
Voyager 205 info
as the info above implies the router should be able to cope so im guessing that the hub is the issue

anyone have any opinions?

Thanks
Jake

cheers for your reply i had a feeling this would be the case but i have a switch on the way anyway which should be arriving today so ill give it a try anyway then ill try putting the comp straight onto the internet via zipb mode on the router i very much doubt its a security software issue i run very minimal stuff on my comp