Integrating a map service into MS CRM with mesh-up technology is not very hard and can add very strong functionality to the users/customer. I havn't worked in a project yet that wanted this functionality which is the reason why I havn't blogged about it.
However, today I had a look at the CRM Team blog and found that Ayaz Ahmad, a CRM MVP has written a blog entry on how to make a simple CRM integration with Microsoft Mappoint.
Please have a look here if you are interested:
I am not sure how well MapPoint works in Europe/Northern Europe but I don't think integration with Google Earth (sorry MS, I know you hate them :) or other similar services (www.hitta.se, www.eniro.se) is very much harder as long as the do have a wsdl-webservice that can easily be consumed, or can easily be configured using URL-parameters.
Anyway, start off with MapPoint, if it doesn't go all the way for you, try working with some other Map Service supplier. There might also be some nice ActiveX-based map-service if a better map GUI is needed.
CRM and SharePoint Consultant