Domain To Workgroup

This has to do with Windows XP Pro. I joined a Server 2003 AD domain. Then I wanted to be a member of a Workgroup. Rather straight forward. My system became a member of the Workgroup but I can not brows or even ping the two XP Pro systems that were members of the domain and now are members of the Workgroup. I have another XP Pro system that I did not join the domain with and it can see all systems in the Workgroup. Any ideas?