Overclocking my 7900 GT, begging 4 help

First off I greatly apologize if I come across sounding like I have no idea what I'm talking about. The truth is I really don't. This is the first time I've braved into the overclocking world & as with most n00bs I can't tell if I'm tiptoeing or stomping thru the tulips so-to-speak. I came here because i know you follks know your ****. So if I've screwed anything up or left any important info out please let me know & I'll rectify it asap.

After successfully OCing my Core 2 DUO E6400 Conroe to 3 Ghz (I know I can push it more, just not quite ready), I am finding that OCing the GPU is not quite the simple task I'd hoped for... or it is & I'm just making too much out of it.

My card is the MSI 7900 GT with a stock core clock of 500MHz & memory clock of 1530MHz. I am using Riva Tuner to adjust my clock speeds & ATI Tool to test my rig. The very first question I have is one that has confused me most. Since I started seriously trying to OC my memory has read well below the specs on Riva & ATItool. Starting out it read it was running at 765. Now that could be a cause from when I was attempting to use Nvidia's D.O.T. (Dynamic Overclocking Technology) & after having to reboot because my graphics went haywire I'm thinking it may have reset it to a "safe" level rather than the original stock setting. Now though Riva shows a max adjustment of 1150 MHz.

As of right now I have bumped the core up to 544MHz & memory to 959MHz. Sitting idle I am running at 54 C, Using ATItool's 3D deal I peak at 89 C. My main question is this. Am I going about this wrong because I had my Memory at the wrong (low) setting to begin with and has that caused me to bump my core higher than I should while sacrificing too much memory? If so, how can I go about resetting my memory to the stock speed so i can start over right and once I do get into the OC again where should I start to consider stopping temp-wise before I need to look at some better cooling options?

ummmmm end of the day the card wont do any better - you can overclock the core speeds and memory etc, you CANNOT improve the shaders/pipelines, memory interface etc - at the end of the day its still a 7900GT (24 pipelines, 256 bit memory etc)

BTW video cards are alot easier to kill then any other device (cpu, memory, motherboard) in your system!

If you are using the newer nvidia drivers, they have a power saving feature to slow the clocks down when they are not needed. they should go to full speed automatically when needed.

Yes.

It crashes.