well thanks for link to the corsair website and the one they recomend for this laptop is 150 dollars at newegg which is alot more then i want to spend but i did find a corsair valueselect 1gb ddr2 4200 for $99 what u think?
ValueSelect is a much lower quality module than Corsair's excellent premier lines. Something like Kingston's ValueRAM would be in between the two in quality. Lower quality memory will be more likely to be incompatible with your notebook, if only because it is less likely to tolerate variances.
Your problem is unlikely to be due to a speed difference in the memory, because faster memory can always be run at a slower speed without problems. You are also right that all the memory installed will run at the speed of the slowest memory installed.
However, DDR2 for notebooks is a new memory technology that isn't fully mature, and was less so when your notebook was designed. Thus, your notebook is more likely to have incompatibility problems than are more recent designs.
The key issue here is who shoulders the financial responsibility if the module doesn't work with your notebook. If you buy a module from a site that guarantees the module will work on your notebook, then the vendor is responsible, otherwise you are. Unfortunately, because of the factors I mentioned above, chances of incompatibility are fairly high in the DDR2 notebook market, especially for low-end modules.
There are many different vendors who will guarantee that their module will work with your notebook, so shop around a bit before deciding which route to take.