Hey,
I know this may sound lame, but I really am not sure. I have a Toshiba Satellite L45-54687. It came loaded with 1024MB DDR2 SDRAM and says that both memory slots may be occupied. Maximum capacity 2048MB. I want to buy some more memory to put into the second slot but not sure how much I can buy. Does this mean I can only buy 1024MB more (1G) or can I put a 2GB memory card in the second slot? Thanks for the help cause as you can see, I really need it!
If the Max capacity is 2048, than you are stuck with one more 1024 addition.
Before you buy anything, check if they populated both slots first, usual practice.
PS
I just checked Toshiba specs for their Satellite Notebooks and it is really not clear if they talk about capacity per slot or overall. Usually by saying MAX capacity it means all.
The best is to check with place you purchased your laptop from or on Toshiba help.
PS-PS
It looks like the Max is for total memory. In their specs for U400 machine it is more clear.
I was afraid that was what it would be. Thanks for the info and I will check it before I buy. I don’t think that it is populated though because it is running rather sluggishly. I am hoping to speed it up a bit. 
Make sure that you get the same memory as you can’t mix them
What do you mean by the same memory? The same brand?
You want to make sure you get the same voltage, and same mhz. If yours is 533mhz, you want to make sure that the new memory is 533mhz.
oh. okay. Thank you.
Download and run PC Wizard (free).
http://www.majorgeeks.com/PC_Wizard_d3846.html
It will tell you how your slots are populated without opening your computer and if there’s an SPD chip on them you will get mfr info too.
If you have one slot presently populated with a 1 gig stick, then try to match that for dual channel enablement, as previously mentioned.
If you have 2 x 512MB then you will have to start over if you want 2 gig.
Go to a major memory supplier like Crucial, Kingston, Corsair and use their [B]memory configurator[/B]. Enter the appropriate info in the fields and the correct memory module part numbers (for your comp) will be shown.
Once you have the correct part numbers in hand you can go shop at a reseller of your choosing.
With a matched 2 x 1GB module set, make sure that [B]dual channel[/B] is enabled in your BIOS, if that option is present.