I would like to buy/make a cable that will have a USB
> connector on one end and an RJ-45 on the other.
If by "RJ-45" you mean an 8-position modular connector wired to carry an Ethernet circuit, you'll need an adapter such as Planet Technology Corp. Model PT9500. I have two of these devices in service, connecting oldish PCs (W98) to a Linksys router. They work great.
L-Com sells the adapter, including the software driver (3.5" floppy), for $29.00. See
formatting link
.I'm not sure if it is as easy as cutting off a connector
> on the usb and just terminating the RX/TX/GND like you
> can do with a serial cable (DB-9).
Ethernet uses balanced circuits, whereas EIA-232 (formerly RS-232) and EIA-574 (same voltages as EIA-232, but implemented with a DB-9 connector) use unbalanced circuits. It takes more than just a different connector to make the transition between balanced and unbalanced.
Neal McLain