I have a Myguide sat nav system with maps that areolder than gods dog. Is there any way of updating this or do I have to buy another model altogether. Thanks in advance.....

You can replace the original software with another to get the latest maps, iGO 8/Primo is a popular alternative.
Use the forum search function, There are loads of threads about these devices...

I have tried some of the stuff like copying map files but to no avail. In windows 7 I can see the directory structure, but don't know which files to copy over as the satnav doesn't seem to do anything with the sd card

If you just copy "our" maps to the device then it won't work, You will need to replace the navigation application, It is just a case of replacing the existing app folder with one from this site, and renaming the new folder and application.exe to match the original, Then tweak it to run on your device with your required maps

I have all the iGO stuff on the sd card. Which "apps" folder is it I should replace? Sorry if I seem to be missing the obvious.....

The iGO stuff that's already on the device, Is it the original software for the device? Is so then replace the whole folder with one from this site, be sure to rename the folder\file.exe to match the original so the device can find it.

There does seem to be some igo stuff on the device, but when I change the .exe file I get an error message on start up. I don't want to delete all the original folders, but would that work?

Sorry, that doesn't sound quite right. I'm assuming the device is like a computer, so if I remove all the existing folders and then replace them with the igo folders on the sd card, would the thing start up? As long as the existing folders are backed up of course.

Backup the device to your computer first.

The device is similar to a pc, but it is only designed to run one programme, So you need to trick the system to run something else by REPLACING (the new programme must have the same folder\file.exe names) the original programme, In most cases you can't just install programmes like on a pc, Sometimes you can exploit the upgrade procedure by having certain files on a SD card instead.

Hopefully that explains it a bit.

I have tried copying the files using original names, but when I start up, the MyGuide launcher comes up with an error message concerning ctype.dat. Which file is the MyGuide launcher so I can edit it to the new settings?

Before you do that, Read this guide, some MyGuide device's are similar hardware to Binatone's, It may utilize SHELL.ini to launch another application.