Access other computers on router

[JayScore]

Hello, This isn't a Sky problem, I think, so if posted in the wrong section, apologies.

Got the new router with the smiley face. Signed up in December 2012.
Got two computers connected, cabled, and both show up as connected (CABLED) when I access the router - when both switched on, obviously.
1. Desktop. Windows 7 Home 64 bit
2. Laptop. Windows XP Home 32 bit
Both connect to the internet without any problems when either or both is/are switched on - the router's doing its job just fine.

I have tried everything to access each computer from the other with no success.
I've Shared the root folder of C: on the laptop, and Shared everything I can find how to on the desktop .
Network map on the Desktop (Win7) does not show the laptop, and, equally, the Desktop computer does not show up anywhere on the laptop. I can find no way to find the other from either.
Attempting access by IP address from Run or Browser fails - odd since accessing the router by address happens instantly.

I've tried lots of advice from the net, but the computers continue to refuse to acknowledge each other's presence - on the same router!
I know one computer can access another via the internet - seen such in action, but I don't want to use the internet to access the computer in the other room - "sledgehammer" and "nut" spring to mind. Frustratingly, almost all of Windows' Networking Help, including Sharing, deals with internet connections, access from outside - same with Google searches, and not the connections that exist within the confines of the router; typing any query in Help & Support with "Router" returns nothing. It's as though Windows only sees networking queries as queries concerning connecting to the internet.

Does anyone know how to do this evidently impossible thing. It shouldn't be this difficult. This is a massive failing on Microsoft's part - either in facility or information. I have two computers recognisedly connected to one router, and the only way I can transfer/copy files
between them is by bunging a USB memory stick in one, copying the files, walking into the other room and bunging it in the other computer - OR via the internet - I haven't tried that yet, though, stupidly, it's seeming the easier option. I can access websites across the entire planet, but can't access the computer in the other room - on the same router/network!

Help appreciated.

[seawright]

Can you ping one computer from the other and vice versa using their IP address?

[steelysteph]

Have you put them on the same workgroup? Microsoft have a good guide here Networking home computers running different versions of Windows for networking different versions of windows.

[Isitme]

The most important thing is having them in the same Workgroup. XP and Win 7 have different default names for the Workgroup, so they will not connect out of the box. Make them both the same, 'Mynetwork' maybe, enable sharing on both and you should have no problems. You might find it easier to create a Share folder on both PCs, rather than sharing the root.