I want to upgrade my HP Pavilion dv 1331se notebook's ram. HP's site says that it takes DDR 333 RAM. I want to know if this is just because HP is cheap and doesnt want to put DDR 400 in the notebook or if it specifically needs DDR 333. The notebook has a 512 stick in it now and i was also wondering if I could add a 1GB stick and run my system with 1.5GB of ram or if that would cause a problem. I don't know much about RAM and need some advice.

ram is funny, not funny ha ha, funny strange. your board is designed to use 333 ram, the board also dictates how much ram can be installed in the laptop. for more detailed information about the types and brands of ram, please re-visit hp's website. some laptops are VERY picky about the type of ram you put init also, compatibility is really sticky with them, so dont stray too far fom the manufacturers recommendations about brand and frequency.

Try e-mailing HP they can tell you the best ram to upgrade their laptops with.

Run Everest Home 2.2 and it will give you the spece on the memory you are currently running.

To address (no pun intended) one part of your question, PC400 (aka PC3200) memory will work just fine in a system that calls for PC333 (aka PC2700). This is analogous to putting premium gas in a car that calls for regular. It sure doesn't hurt, but it doesn't make the car run better either. Nowadays PC400/PC3200 is much more available than PC333/PC2700 and so costs less. Such is the computer industry that older parts actually become more expensive over time than newer faster parts due to the older parts going out of production.