Vista is just poor at Networking, Intermittently Loses Network Paths

Hi:

I have shared folders between my office PC and my laptop PC. When the laptop
PC ran XP Pro, I could create a shortcut of the folder on my office desktop
and reliably access it when my laptop was plugged into the network. My
laptop at that time was on a different subnet because it was using DHCP and
my office computer had a static IP address.

After purchasing a laptop with Vista Home Premium, neither computer could
find each other on the network, so I had to use a static IP address for my
laptop so it would be on the same subnet as my other computers. Strike one
for Vista.

After configuring the permissions and shares so I could access the shared
folders from either computer, I again created shortcuts on my desktop for
the shares. They worked fine last week. Without changing any of the shares
and file permissions, the shared folders are not accessible this week and
generate another vague and general error message that the network path is
not found. Strike two for Vista. Yes, the laptop was plugged into the
network and can access the internet.

I can find my vista laptop in my network neighborhood on my xp office
computer, but opening that computer fails with the same error. Strike 3

So here is my question? Why would networking work one day and not the next
if there were no changes made to the system by me the only user. I did take
my laptop home where it worked fine on my home network over the weekend. I
would expect that it would work the same on my office network the following
week.
Any help will be appreciated.

Thanks in advance,

Pete