Partners Laptop loosing connection to network drives.

Hi All, We have 2 laptops in the house and one xp desktop machine,

Both Laptops are Win7 64bit.
The XP Machine runs like a server sharing one 3TB External HDD and one 80GB internal HDD
The XP Machine is Wired and the Laptops are Wireless.
On my laptop I can Access The Hard drives and use map network drive to use them in my computer.
On my partners laptop I Do the same but then her laptop drops the connection and cant access the Drives.
She can no longer see the XP machine in Network computers and she has to restart her machine and I restart the XP machine in order for the Network drives to be seen again..
The drop in connection happens randomly but often enough to be really annoying.

My laptop never looses the connection regardless of how much I use it..

I'm stumped.. Any help would be very appreciated..

anyone??