Yahoo instant mess and wireless connect

I have 2 wireless laptops and 2 desktops using ethernet cableing. I use TimeWarner cable with Roadrunner. Cable modem is connected to Microsoft MN-700 AP and Access Point is connected to 3COM SuperStack II 12 port switch. Laptop 1 has MN-720 card WinME. Laptop 2 has integrated wireless WinXP Pro. Desktop1 is located in a back bedroom and wired through to the 3COM switch. When ever
my Granddaughter gets on Desktop1 and uses Yahoo instant messenger the laptops are knocked off the network. any ethernet connected PC’s stay connected fine. Wireless is fine as long as she does not start YIM. I am puzzled. Does it have to do with Bandwidth? Or is it a Switch/ port problem? Thanks