Poor speeds -:- Wireless issue

[alferret]

Here is the spec of the hardware.
Belkin F5D8233-4 Wireless 'N' router (latest firmware)
Rebuilt C2D desktop running Vista 32bit Home premium fuly UPD with a TP-Link WN851ND PCI wireless card (also used a Tenda N300 PCI wireless card which is being returned to ebuyer same if a little worse results)

When the desktop is in the same room & about 3ft from the router we get excellent Mbps throughput (full 20Mbps)
Move the desktop into the dining room & the aerials on the desktop are less than 9ft from the router then the speeds, be it through a speed test site or downloading a distro from usenet the speeds drop to <3Mbps on the Tenda & <6Mbps with the TP-link. Yet both of our laptops & both phones (SGS2 & SG Note) can download at the full 20Mbps at the same or quite close position to the desktop.
I have turned off QoS packet scheduler, connection strenght is always excellent & 85-100%
I havnt disabled IpV6 (yet)

The router is mounted on the adjacent wall to the dining room about 3ft off of the floor, the wall is plasterboard/brick construction.

Tried netstumbler but doesnt recognise either wireless card.

Tried all available channels with no increase in performance from the desktop (or anything else)

Any idea's or suggestions would be more than appreaciated & if any further info is required I'll post it.

[alferret]

Fixed the poor speed issue
You'll not believe how/what was done but I now get full speed.

[danielf]

I don't believe you...

[alferret]

I wouldnt believe me either lol!

Got the SH yesterday & that has given me full speed on this desktop! Its an Arther C Clarke moment, you know an Unexplained mystery