They're all connected to the internet but aren't able to talk to each other. I'm having difficulties in logging in to the other computer to access it.
In Windows I use this to access the network.:
run \\192.168.0.123
In Mac I use this to access the network.:
smb:\\192.168.0.123
From my Desktop and MBP I am able to connect to the 2 Dell laptop. I'm just not able to access my Desktop and MBP from any computer or laptop. When I'm trying to access any of the two it will just ask me for my "Account Name" and "Password" but will not accept it. I've tried simplifying my password and account name for my Desktop and MBP so I wouldn't get a typo error. But still no success.
All PCs are running in Windows 7. Two Dell Inspiron 1440 and one Desktop Computer.
My Mac Book Pro is a Lion (Mac OX 10.7.2).
Below is a diagram ofhow my computers are connected.

Here is an overview of how their connections work and fail:
- MBP -> 2 Dell Inspiron 1440 = success!
- Desktop -> 2 Dell Inspiron 1440 = success!
1 Inspiron 1440 -> 1 Inspiron 1440 = success!
Inspiron 1440 -> MBP = fail!
- Inspiron 1440 -> Desktop = fail!
- MBP -> Desktop = fail!
- Desktop -> MBP = fail!
What do you think is the problem? Do I miss some permissions settings or something?