Vista/xp Computers will not talk to each other?

Hi

I have the following:- Vista x64 laptop, Vista x32 Desktop, (Wifes)Dell Win7 x64 laptop. All running on my home network. Cisco/Linksys x3000. I also have an Old Toshiba laptop running xpPro, which I wish to add to the network for monitoring 2 Ip camera`s remotely.

The Issue is:- The 2 Vista machines can access each others files, printers, even the i-pad! etc. BUT niether will "talk" to the Win7, nor the xp machines. The Win7 machine will "talk" to the xp macine and vice versa BUT not the 2 Vista Machines!!!.

Pinging the machines, using the DHCP client table ip info. 2 vista machines can "see" the other but not the Win7 nor xp machines. and vice versa. I am begining to suspect the issue may be with the Router? but why that should be? I am at a complete loss?

The Win7 (Dell) is running McAffee (Pre-installed by Dell) the 2 Vista Machines have the latest Norton (NIS) the xp machine has (as yet) only the windows Firewall etc.

Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft® Windows Vista™ Home Premium, Service Pack 2, 64 bit
Processor: Intel(R) Core(TM)2 Duo CPU T6600 @ 2.20GHz, Intel64 Family 6 Model 23 Stepping 10
Processor Count: 2
RAM: 4089 Mb
Graphics Card: NVIDIA GeForce 9600M GS, 512 Mb
Hard Drives: C: Total - 450940 MB, Free - 154627 MB; D: Total - 25984 MB, Free - 6825 MB;
Motherboard: MEDION, P6618
Antivirus: Norton Internet Security, Updated and Enabled

pete