Notices

I take it that this is improbable and hard to do

I've used GPX View. It's for geocaching, but if you can find data for your golf course somewhere, you can convert to the proper format.

However, I haven't found the GPS in my N900 to be accurate enough for my (poor) golf game. The accuracy bounces around even if standing still. Anywhere from 16ft to 62ft (or something like that), anyway, not necessarily good enough to choose the proper club. I do have a bluetooth GPS that give much better results, pretty steady in the 10-16ft range.

I think you can get it to download maps to see where you are, but haven't used it much, as it can be a little work since it's not really for golf.

I realise this is very late after the OP's request but I am posting it here in case it is of any use to anyone else. I have had some success getting FreeCaddie's Jave version to run on the N900 thanks to packages from other people.

First, I installed IcedTea and MicroEmulator to have Java support.

I then followed the instructions in this forum post about setting up the javax.microedition.location port. I used the TAR file from the post but there is also this garage page for OpenLAPI (I actually did this after I had got the app running as I found that GPS was not working - this gave me GPS access)

I then grabbed the MicroEmulator skins from this forum thread. The first skin appears to be the more functional but the larger one posted later in the thread makes it a bit easier to use FreeCaddie.

I then downloaded the JAR and JAD files for FreeCaddie for Jave.

I placed the skins and the JAR and JAD files on the micro SD card but you just need them in an accessible location on the N900.

I then ran this script to start MicroEmulator with the FreeCaddie's app ready to run, just press OK on the UI and the app is loaded:

You can then follow the FreeCaddie (Java) Tutorial. On page 3 of this I needed to check "Use extra GPS settings" and then I gotr a GPS fix.

Note: The fonts on MicroEmulator are quite small. You may be best served to start MicroEmulator first and then select the skin (device) you have copied (240 x 320). The phone skin that comes with MicroEmulator is probably the best for entering text if you choose to buy the Pro version. I set the larger skin (640 x 360) that I copied as the default and this made it easier to use the FreeCaddie app.

Since this caught my eye again.

You can use nitdroid, a bluetooth gps, and an app to get an external gps working with nitdroid. From there you have quite a few golf apps to choose from.