Whoa first post in over 3 years... Holy fuck... Anyway nowadays I'm a happy owner of a Nokia n900. And I used to have the problem of greasemonkey not working. Eventhough I installed it properly from the repositories it wouldn't wok or show up in the addons. I reinstalled it countless times, uninstalled adblock just in case there was some compatability problems, rebooted many times as suggested in maemo forums. Nothing worked until I finally figured out how to solve it.
So here's how:
1. Uninstall greasemonkey and adblock plus if you have it.
2. Reboot the phone.
3. Install CuteExplorer (or you can just do this from the x terminal)
4. Delete contents of the following folders:
5. Install greasemonkey and adblock plus
6. Reboot 2 times and voila you're done!