Shared Mac won't connect first time

Hi

I have an iMac and a Mac Book Pro both running the latest version of Leopard.
They are also both connected to my wireless ADSL router, the laptop wirelessly and the iMac via an Ethernet cable.

Once both machines have been switched on for more than a few minutes an icon appears in the Finder indicating that each machine is there to be viewed as a shared device.

Now if I click on the icon to view the contents of the iMac or laptop (works the same at both ends) I have to wait about 3 minutes and then Finder displays a message saying that it couldn't connect.

At this point if I click the connect as button the finder throws up a login dialogue almost straight away prompting me to login as a guest. I provide the correct password and then it connects straight away.

Is there a way to stop this? so it just connects first time?

Just out of interest both machines have the same user name and password, could this maybe have something to do with it?

Its just a real pain, when I use the same process to connect to my Windows PC the finder just connects straight off.