This sounds ridiculous but you guys have pulled through in the past... The concept is straight forward; use the n810 to connect a pc to the internet via a usb cable. This feature would be fantastic if at all possible!

The trick would be getting the pc to recognize the n810 as a network adapter...

...which is going to depend on what OS is running on the PC.

See here
Under the section Configuring the host as a gatweay there are instructions to configure a Linux host pc as the gateway, in theory you could do it on the tablet instead (provided iptables is available on the tablet, which I doubt), and manually setup the network on the pc to use the tablet as a gateway and use the same dns server the tablet is using.

i betcha windoze won't like that

No, but you can flash this kernel and use ICS.

As long as usb networking works, windows doesn't care, just set it up manually.
The problem is, I don't know if the tablet has iptables and the required modules for masquerading.

Edit: if I didn't misunderstand, the OP wants the tablet's wifi connecting to the internet, and attach a pc to the tablet via usb to "use" the wifi connection, and that's what linux boxes have been doing for ages.

As I suspected, the tablet is missing many iptables modules, so it's not possible to masquerade traffic from a pc connected via usbnet.

There are a couple of alternatives though:

You can install privoxy on the tablet and use it as a proxy from the pc (just configure the browser on the pc to use the tablet as a proxy (using the privoxy installed there - untested)

The method I tested (so I can confirm it works) is to use the ssh server on the tablet (I had openssh already installed).
On the pc, you ssh into the tablet using dynamic tunnels, e.g. (using the addresses on the wiki page)

(if you're using windows, I'm not sure that putty has an equivalent option to -D edit it has, just mark the "Dynamic" option in the ssh tunnels panel).
Once the connection is established, just configure the browser to use a socks 5 proxy pointing at localhost port 6969 (with firefox is under advanced settings, network, parameters).
You can use any other program as long as it can work through a socks 5 proxy.

Ya.. I know that,but i.m using XP and it just recognise my n810
as a RNDIS/Ethernet Gadget, pops up a window asking me for
a suitable driver which i don't what it is..

http://wiki.maemo.org/USB_networking#Requirements