Horizontal lines problem when in X

Hi, I've a new Inspiron 5150 with NVidia FX GO 5200 installed. I'm using Debian Lnux (Sarge) with kerel 2.4.22. I get to load the module correctly (both with agpgart and native nvidia agp) but always get this annoyng problem:

When I get to X (I run startx) some horizontal disturbance lines make their presence felt with increased frequency over time. I have no problem under Windows, so I believe it' s something in the configuration or kernel options. The module is loaded, since I can see the sawfish command and all. Just these lines that make my life impossible after 5 minutes or so.

The problem remains when I get out of X and disappears only if I reboot. When I do this anyway, the problem is not present in the shell, but is felt as worse as ever when I try to reenter X.

It seeems the only solution is to halt the machine for 20 minutes or so, but this to get 5 minutes of usable X time... this is no solution at all! I start thinking this has something to do with cpu heat control or fan control with the nvidia card, but I also believe it's software related, since I get no problem at all under windows (and that's all graphics!)... Anyone has any ideas? I just need some track to fllow, since Dell isn't providing email help due to "technical difficoulties" and I can't phone since I have truly horrible work hours...

Thanks for all the help you can give me!

Physis77