Problem solved, thanks for the tip anyway.
Turned out I was using the wrong drivers, should use rt3070 not rt 2870
Following the guid on:
it all works fine (yes it is in france, which I don't know either, but I could follow it anyway :-))
some notes for others that want to do the same:
when unpacking the downloaded file:
tar -xvjf 2009_1110_RT3070_Linux_STA_v22.214.171.124.tar.bz2
the resulting file is also a tar that needs to be renamed and unpacked, when doing so you get the directory as described in the guid.
The device lines that are described to be in os/linux/usb_main_dev.c
I found in common/rtusb_dev_id.c but the required rows were already included.
after the installation and restart of networking, I had to bring the wireless interface up in three steps to get in to connect correctly with dhcp:
1. ifconfig ra0 up
2. iwconfig ra0 essid name
3. ifup ra0
added these steps in the /etc/network/interface file:
iface ra0 inet dhcp
pre-up /sbin/ifconfig ra0 up
pre-up /sbin/iwconfig ra0 essid name
This is probably not the best way to handle the configuration, but it works. I have no clue why it's not enough to specify the essid row.
If someone has a better/more correct way of doing this, pleas let me know.