HP laptop puts the model on the LCD panel, either at top right or bottom right corner. In my case, my laptop is HP331, but the real model is shown on the bottom right as Compaq nc4400.
This model uses DDRII memory modules. The memory can be either 533MHz or 667MHZ. They have model name PC2 4200 and PC2 5300 respectively. So if you want to expand your laptop, just look for the two types of memory modules and plug in and here you go!
