A couple of questions about upgrading.

Because 64mb is being used by your motherboard for onboard video and yes if you install both the 512 and the 256 you will get 768MB of RAM minus 64mb for the video.
If you install a graphic card you have to disable the onboard video and install the drivers for the new video card. Disable-Onboard Video Guide

 

Most likely, you have an integrated graphics card that shares 64MB of the main RAM. Hence, 512 - 64 = 448. You should be able to install both the 256 and 512, which would give you 512 + 256 - 64 = 704MB.

Regarding the graphics card, unless your computer is really old, it should have either a AGP or PCI-Express slot. Find out which one it has, and buy a video card that works for that slot.

 

Is th RAM the same type? Find out the PC type of the ram (e.g., PC2700), the RAM speed (e.g., 333 Mhz) Look at both the sticks and post the details on the labels.
You can get the video drivers on the net what type of video card is it?

 

Yeah they are the same should work ok

 

It really doesn't matter what brand RAM as long it fits and is the right pin type. The PC# appears to be different so I don't think it will work(Not sure about this). You can mix RAM, but it is most recommended to get both of the same size. If you buy the same RAM sticks that are compatable/say they are dual channel compatable, you can use Dual channel, but I really don't know what that does or what the advantages are. Though I have been hearing Crucial is a good brand. I think I'm using a Samsung 512 MB with a Patriot 2 GB both at 533 MHZ.

 

Quick answer no it use's a different type slot.

@TheWingless It does matter if you put in 1GB PC3200 DDR400 and a 256MB PC2100 DDR266 you have to put he PC2100 DDR266 in the first RAM slot or the PC would not use it and the PC3200 DDR400 will run at DDR266 speeds so you would better off only using the DRR400 at full speed. The Brand is not importent but the Type and Speed is.

 

Oh really? I never really knew that, but I'll make sure to be careful of that. I did a lot of research before buying my RAM though so I didn't run into any trouble. Probably just best to buy them in pairs or memorize the last RAM stick you bought so you can match it up. Both of mine are the same speeds so it's perfectly fine over here. I'll probably buy a another 2 GB if I ever need it to replace the last 512 MB I have. BTW, what is the PC# for...? Is it speed, or does it even affect is physically?

 

You can find all the information on DDR ram here http://en.wikipedia.org/wiki/DDR_SDRAM

 

No sell it on ebay it is old SD RAM you are using DDR RAM it uses a different type slot.