WiFi problems with BelkinBelkin F5D7130 and Dell notebook

I have purchased a new Dell Latitude D800 with built in WiFi, following a
theft of my previous notebook that had a Belkin WiFi PC card installed. The
old notebook performed fine. The new one with built in WiFi performs like a
dog.

My newly reinstated WLAN is running rather slowly, despite all indications
(signal strength etc.) being good to excellent. It used to run extremely
fast when I had my old laptop with a Belkin WiFi PC card. The wireless is
set as my primary connection so, even if I have the cable connected as well,
the PC runs slowly. Here are the full system details:

PC
Dell Latitude D800 with factory installed Dell TrueMobile 1300 802.11b/g
mini-PCI card

I have tried to download and install the latest driver for the TrueMobile
1300 from Dell's website (R65194.exe) but although everything seemed to go
OK, I am not convinced that the driver has updated - the driver details
visible via Device Manager have not changed. They are: Broadcom driver dated
13/6/2003 version 3.20.23.0. The latest driver from Dell is dated 20/8/2003
which is what makes me wonder.

I have ZoneAlarm running on the PC, along with the TrendMicro OfficeScan
virus checker. The Zone Alarm settings for the Wireless adaptor are exactly
the same as they are for the NIC.

Currently, I have Windows XP handling the wireless connection. I have tried
it with this option off, but with no noticeable difference

Access Point
This is the Belkin F5D7130 with updated firmware version 2.00.01 (which I
believe is the latest). The boot version is 1.03.08

It is plugged in to an ethernet port which is connected to the 10/100Mbps
switch. The AP successfully detects that it is connected to a 100Mbps
ethernet. The AP can be successfully pinged at around 24ms (the first ping
of the 4 is slower, but the last is always in the 24ms range)

The AP is set up with 128-bit WEP. It supports WPA and I would prefer to use
that, but the Dell unit does not appear to support it - though Dell Forum
entries suggest that it should. It is possible that I don't have the correct
update from Microsoft installed.. The speed is not noticeably affected by
whether the WEP is on or not.

The AP is also set up with MAC address filtering, allowing my laptop and a
specific Belkin WiFi PC card to connect. Again, turning this off does not
make a noticeable impact.

The AP is set to channel 6 and the 54g standard is enabled

The AP is set up not to broadcast the SSID. Again, broadcasting the SSID
does not seem to make a difference to the speed.

Any help would be greatly appreciated.

TIA

Maurice