1. how far away from the AP is your car's antenna?
2. is there anything in between the two like electrical wiring, steel doors, etc that may be causing interference?
3. are there any other devices that use the 2.4Ghz band operational while you are trying the link (microwaves, wireless cameras, cordless phones)?
Those will affect your throughput. You are at least gitting a link, which is a good sign.
The USB ports on the m10000 are USB2.0. WinMe does not natively support usb2.0, so you have to download the drivers here