If we can assume these systems are all in the same Workgroup or Domain there is a fairly simple way to get the information by calling NetRemoteTOD() of the netapi32.dll library.
I dug up an old example/demo and have attached it.
Edit:
I should add that this probably won't work at all for asking a Win9x machine it's current time and date. Also if you call NetRemoteTOD() on an NT 4.0 (or earlier) system the server name must be in UNC form, i.e. preceded by two \ characters:
\\BigServer
On newer systems (Win2K and later) you can use either a DNS name or a NetBIOS name, and you do not need the leading "\\" symbols.