Actually you can buy Serial to USB adapters. They are used to connect legacy
devices such as GPS etc which use a PC serial port connection. The adapter
is used to connect to a laptop, for example, that has no serial connector.
In the UK these adaptors are a costly 30 squid. Just thought it may be a
simple task to make one and save some notes.
It's not just a matter of connecting a few wires together, it would be
far more time and cost-effective to buy one ready made even if you
already had enough knowledge to built it without asking in the first
place.