Why does higher refresh rate mean loss in quality?

I am experiencing a strange problem with my V7 22" Diamondtron monitor.
I am running Win2k with sp2 and have a screen resolution at 1024*768 and a refresh rate of 75mhz (I have the specific manufacturers drivers for the monitor installed).
The problem is when I increase the refresh rate the picture is not as crystal clear as it is at 75. Any characters on the screen appear slightly blurred.
I tried increasing the rate to 120mhz (which the monitor quite happily supports) and also installed nvreffix and set it to 120mhz (I have a CL Geforce DDR) but still blurred.

Anybody have any ideas?

Thanks in Advance,

A

Oh BTW:

System:
Athlon 800 Classic (not o/c)
Asus K7V
CL GeForce DDR
256 meg memory
Highpoint Raid HP370 Controller (I know this can cause funny things??)
SB Live! Value
Win2k SP2