Best wireless G adapter for range

Hi,
We have changed over to a Verizon MiFi wireless router that makes cell network internet available via a built in G wireless router for up to 5 computers.

The MiFi is working on fine on the PC located near it (its a huge improvement in our internet speed), but, I am having trouble getting the PC that is across the house from the router to work reliably due to low signal strength.

Can anyone recommend a long range wireless adapter for the distant PC?
The PC has both USB and internal slots available -- so it could be a card or USB plug in.
It runs Vista 64.
I believe that the MiFi only offers the G (not N) service.

I not a fan of having to tinker with things for hours to get them to work, so something that comes out of the box, plugs in, and runs without a lot of fuss would be nice.

Thanks -- Gary