With nRoute you can use the current City Navigator NT maps in classic MapSource format. Therefore it is necessary to convert a gmap version with JaVaWa MapReverseConverter into the old format. This conversion is possible without loosing any data.
Note: if you want to use the European map, don't take the Unicode version - only "normal" NT version supported!
You also can try
[Please Register or Login to download file] . Some of them are available in classic MapSource format - so you needn't convert them.
Another possibility to use Garmin navigation with a Windows laptop, but also outdated, is Garmin MobilePC. With MobilePC you can use current map images up to a size of 2 GB.