*edit: problem now solved by enabling DHCP.
Thanks to everyone who contributed with all tips and tricks here. I have now flashed my phone to WM2005, and it seems to be fast responsive. However, I have one (at least for now) problem. Activesync won't recognize it. I have reinstalled Activesync 4.1, deleted the previous phone connection and restarted both my computer and my phone several times.
The thing that really troubles me is that when I connect the phone, my computer recognizes it as a network card operating at 10mbps, and tries to aquire an ip address from it.
I'm on a 6mbit dsl connection with a static ip on my machine, so I really don't need gprs for surfing. Any tips?