I suggest you read the
PCMech Networking Articles. The short answer is that a private network hooked to the internet via a dial up connection can run very slowly depending on how many people are on the line and sharing the same connection. It's not the connection that slows the network down, its the active sharing of the available bandwidth. You can get the same effect with cable. If it is the middle of the night and everybody has gone to bed your cable connection to the net is super fast. If it is early evening and 80 other people are on line the connection seems very slow.
CH