Gday Steve
The LX200s use serial comms ( rs232 ), not USB.
If you dont have a real serial port, you will need to get a USB to serial converter. The actual cable used to do the update is supplied by Meade ( as a 507 cable kit ), but you can easily make your own for about $5.
After that, you need a program that can do the updates.
Meade supply their ASU utility,
but a better ( and also free ) option is to use the StarPatch program.
http://www.stargps.ca/downloads.htm
This application is faster and more robust at getting and holding the comms port when doing updates. It also has better error checking.
If you wish to apply patches ( that fix known bugs and add enhancements ) then you really should use StarPatch anyway.
The latest rom files and patches can be downloaded from the StarPatch site, or from the files section of the Yahoo forum that specialises in the LX200s.
http://groups.yahoo.com/group/LX200GPS/
Lots of other LX200 specific info is in the files section of that site, so it is always worth a read.
Andrew