Question about RAM on Toshiba Notebook

Just bought a new PC for the wife. It came with 256 RAM, I figured no big deal I would just buy her a 512 module and drop it in. Then the fun started. I am a real amateur at PC's, but have added RAM to a couple other laptops no problem. The trouble here is trying to find exactly which one to buy. The PC came from Office Depot. When I check the Toshiba site it does not exist. When I call them I get a couple people who can almost speak English, and act like they have no idea what RAM is, but want me to place an order for it, even though they seem to have no idea what I am asking for. The info on the PC says: PC2-4200 DDR2 SDRAM When I look on line, I am finding 240 Pin,and 200 Pin modules for this. I sure do not want to get the wrong one and then try to return it. The model on the PC is M55-S1001. The "Quick guide" In the box is for models M155-S139 and so forth. I think this is one of those deals where Toshiba made this just for Office Depot, but since the "help line" at Toshiba goes to people who can't speak English it's hard to be sure. So Does anyone here know if the 200Pin PC2-4200 DDR2 SDRAM is the right one for her's? It looks like it is, but I was hoping maybe someone here would know for sure before I buy one. Thanks. The E-Mail address here is a good one if you want to answer of list. Thanks.