Networking Vista and XP

I have a new Vista (Business) machine, and an old XP Home laptop.

The new machine is hardwired to a wireless router, and the old laptop accesses the router via a TrueMobile adaptor.

Both machines have internet access with no problem.

The new Vista machine can see the laptop over the network, and access shared drives and peripherals, but the XP laptop cannot see the Vista machine or it's peripherals.

The Vista machine "see's" the laptop in the network "map" but does not place it in the map.

I'm sure I'm missing an easy step, but can't put my finger on it.

Thanks in advance.

Donn

Inspiron 8200, XP Home
Precision 390, Vista Business