I currently have the following
Virgin Cable Modem (wired to Pc) Broadband size L
Netgear WGR614 router (wired to same PC)
daughters have between them
1 PC with Netgear WG311v2 802.11g wireless PCI adapter
1 laptop with intel R pro/wireless 2200 BG
netbook - not sure what this has
If what you have written above is correct all traffic to your daughters has to pass through your PC on the way to outside world and that would tend to slow things down.