I am pretty sure this is all down to refresh rates. I didn't buy my monitor myself so didn't have the manual to hand, couldn't find the manual on the web as the monitor is quite old now, but did find a list of refresh rates that I could use. I found mine at http://www.mail-archive.com/linux-ha.../msg02097.html
just to give you an idea of what to look for, go down to the "Monitor section"
1. I put these into my X11 config file /etc/X11/XF86Config-4 file in the monitor section
2. Restarted the X server, Ctrl+Alt+Backspace
3. Went into configure my computer, hardware and change screen resolution and selected a resolution that i wanted. it then required me to logoff and logon.
The screen was a bit better, but i used the key combination CRTL+ALT+Minus or Plus key on keypad to cycle through the refresh rates. I have managed to alleviate what I think is every last bit of wobble.