Is the DNS resolving?

>Hi,
>
>At home I reinstalled windows server 2008 r2 in our server after difficulties and am now trying to replicate the previous environment which includes using a workgroup instead of domain. However, the server and a windows xp machine cannot see each other. A windows 7 machine can see both the windows 2008 r2 server and the xp machine.
>
>What may be the reason?
>
>TIA,
>
>Alex