Slow VPN connection

In our network (w2k3 domain, and xp workstations) connecting with vpn to the internet is just very slow. Especially loading the the default intranet home page takes much time!

Here`s the scenerio:

- The VPN software client is Cisco VPN client
- Workstations are all XP
- The VPN access server is in Australia, while the branch office is in Tokyo also the INTRANET server is in Tokyo
- The wireless network/data card is Fujitsu AH-F401U

Here`s the problem:

With this wireless connection, when a user initializes either internet or intranet connection, it takes as much as 2 minutes and 30 seconds (2:30sec) for the INTRANET site (default home page) to fully open.
On the other hand with direct LAN (via LAN cable) connection, it takes just about 0.5 seconds to open up the same INTRANET site.
I`ve tried all sorts of work arounds with no success. Including changing the BTU size, and various other twick-settings in the VPN connection, and Wireless NIC connection`s property settings.

Specifically what we want to achieve here is to reduce the time it takes for this INTRANET site to fully load.
Anyone gone through this before? Any solution please?