Hello. I have the same problem with SuSe 8.0, had the same problem with SuSe 7.3, both with stndard kernels (2.4.18 for SuSE 8.0) and with Nvidia drivers down the lane to 28...something. The DPMS just does not work properly. If I use the standard drivers everything is O.K. I tried to discuss this issue here before and there was no solution found. I contacted Nvidia support and I got only the typical saying-nothing answer (we are revising your problem....)
Removing the Option "DPMS" leaves the monitor always on, xset dpms force off leads to invalid sysnc. (with or without the DPMS option in config)
Manli Nvidia GeForce 2 MX 400
ECS P6IPAT Motherboard
PIII 667 Mhz
512 MB RAM
SuSE 8.0, Kernel 2.4.18
Just use the power button on your monitor, that is the only solution I use.