If you don't know the model #, then we need to narrow the search down a little if you want the right instructions. What Processor and memory do you have. To do this, press at the same time the windows key and pause/break key. This should bring up a screen like this:
Just post the info under the `system' section in the middle:
Processor: Intel Pentium 4 CPU
Memory: 1022MB
then we'll go from there.