USB communication

Hi experts;
I have an issu about new generation Laptops. New Books have only USB ports while in our system system some GE PLC 90-30 are installed. The communcation is done via serial rs232 port.
I used many USB to Serial converter but can not able to communicate with the PLC.
Is there any help about this issu?
Please guide me where from i found a USB to SERIAL converter which works fine and never break the communication?
I have no ethernet card on the chasis.
Regards

Use the search tool and Look for keyspan, gurus here say that´s the one.

I Would recommend you to use Quatech ExpressCard Serial Adapter.
It more pricey the other but it the closed to the real thing.
It is not work on USB .It connected to the PC bus.
It work much better then keyspan which I have too.
You need ExpressCard slot on your computer too.

Weldeto;
Can you use this one with GE 90-30 CPU 351 PLC?

jcp, you may check here. Check the bottom of the page.