Some dialup ISPs block the ports or protocols that are needed to create a VPN connection. Beyond that, there is no technical reason you could not establish a VPN connection over a dialup line. For what it's worth, a few broadband providers also block VPN connections, so if that is your main reason for getting the DSL, you may want to check first.
With the dialup, your connection will be slow, I wouldn't expect to browse your network over such a connection without getting frustrated. You should be able to use a remote desktop app or a telnet session. Should also be able to FTP.
You will not be able to use most of the 'hardware' based servers or clients (actually you could with a lot of work, but I wouldn't try it without a really good reason). Where you go from there will depend upon the OS on each side of the connection.