Windows server 2003 should be able to support 64 bit systems without issue. Adding the machines the same way you would with XP or Vista. There is no mention of Home Premium or Pro being an issue.
Interoperability between XP and Windows 7 computers has been a reported problem, but you can go to the microsoft site for those issues.
You may need these downloads if there are issues with adding your four pcs.
Windows 7 Home premium, like all the home versions of Windows cannot join a domain!
You can trick home versions of Windows into thinking they are Pro but it involves editing the registry and is not recommended. Always buy Pro, Business, or Ultimate for clients on a domain