here's some advice from my playing around with this unit - hope its helpful - use at your own risk!
This unit runs windows CE 5.0 and so any software you want to run must run on this operating system. So if you want to run Garmin for example you need the Garmin XT version made for windows- but I don't recommend this as its a huge job to get running. The Igo8 software it came with runs nice.
The Igo8 software mine came with has a full license -if you look in the igo\license folder in the unit you will see that you have licenses for every map in the world (those lic files can be opened as text files) - this makes life a little easier! It means that whatever map you copy into the igo\content folders should run OK
1) Back up what you have !! - hook the unit to the USB of your PC and make a copy of the entire drive called TFAT to your PC in case all goes to hell. You will have 2 drives visible, one the internal memory of the unit (TFAT) and the SD card.
2) Find the map you want online - either through torrent sites (piratebay or similar) or whatever you can find (suggest google search for "igo8 map download" works pretty well - just keep searching, there's loads of them out there.
3) Download and un-zip or un-rar them and they will usually contain a few folders with names like; building, map, poi, and a few others, simply copy the content of these folders to their respective folders with the same name in the igo\content directory on the unit, if a folder you have downloaded is not already there, just copy it into that directory. If it asks to replace files say yes. Make sure you have enough space on the internal drive to copy your map onto it! - if not delete a few maps you don't need and their corresponding poi and building files (you can always put them back later from your backup).
4) Reboot the GPS unit (unplugged from PC) and run the igo software and in the maps section you can choose to open the maps you have just installed. - Should work fine.
5) If all goes to hell, just replace the whole TFAT drive with the backup you made at the start.
You can keep a few maps you want on the SD card too and copy them to the unit once you need them using a PC, they can also be run from the SD card but this takes a few more steps - easier to copy them in to the unit when required.
These sites are useful for further and much more techie advice;