Ubuntu 10.04 LTS offers only 640x480 display resolution after installation

NVIDIA GeForce 4 MX 440,
AMD Athlon XP 2000+ 512 MB
Windows XP already installed.
Ubuntu 10.04 LTS installed on free 10G partition.
Bootmanger is working fine, except from X the system is working fine.
No messages while installing the System.
What else do we need here?

after installing Ubuntu 10.04 on the the above computer the system started with VGA resolution.
System advised to install Nvididas drivers and so I did. Nviidia X server settings program is hard to handle in this mode and does not offer further options.

xrandr output is: Screen 0: minimum 320 x 240, current 640 x 480, maximum 640 x 480.

For XP the card runs on 1280 x 1024 and even higher resolutions are available.

Can anyone advise how to solve this problem?

Many thanks in advance

Wolfgang