I purchased this thingy two years ago off eBay for ~€5.
It provides a way to create "virtual" COM ports on recent computers that only offer USB ports.
The model appears on the serial connector as HL-340.
As for most Chinese accessories, the drivers are not provided
and I first had to spend some time searching the forums.
I'll keep my findings here so you won't need to go through this yourself.
The item sold by DealExtreme is also based on chip CH340 so it should use the same the drivers.
The drivers for HL-340:
Manufacturer page: http://www.wch.cn/download/list.asp?id=65
I've stored a copy on FileFactory as well.
These drivers are compatible with Windows from versions 95 to 2008 R2.
On OS from Vista ansd up, the installation program may not work.
Instead: unzip the exe file (7zip can do this all right),
go to the device manager and right click on the USB-Serial entry,
then select "Update Driver Software..." then browse to the location of CH341SER.INF
This adapter works for connecting Terminal Emulators via COM port.
You use the paper clip test to check that your serial interface is working fine.
It also work fine with the old X10 Computer Interface CM12U that came with a RS-232C connector.