Why do I experience slow application response after connecting with VPN?

The VPN connection is PPTP using ADSL to a Head Office. The Head Office also uses ADSL 10Mbps down, 768Kbps up. There is no problem establishing connection using “dyndns”, but sometimes apps work fine, then whenever I try to re-open the same apps, it is slow to respond.

One database application uses a web browser (IE8 or Firefox) to login but even that has a slow response.

I am thinking that the server may be responsible. (DELL Poweredge Duo Core 3060 Xeon Processor 840 4GB DDR2 667MHz. Can anyone suggest a possible solution?

Anthony Pontiflette