creation of device ttyUSB

[newusermike]

I was trying to sync jpilot using a usb however I did not have a ttyUSB listing in dev so I created one using mknod then created a sym link however my question is when I use the sync to jpilot it only works once and then the node or device ttyUSB1 in dev disappears.

Can someone tell me how to create this and have it remain permanently?
Please post an example or tell me in plain English so I can follow the steps I am new to linux
thanks