If you buy sticks have sticks that say 1gb on them, they're actually 1024mb.
Take a look at this module: http://www.newegg.com/Product/Product.aspx?Item=N82E16820145153
This is marketed as a 1gb module but click the picture to enlarge and go to the second picture. On the right side it specifies 1024mb. 1gb is easier to say than 1024mb and close enough to it, so the computer industry often times refers to 1024mb as 1gb.
The first two links you provided don't work for me, but if you installed 4gb and it reads 4096mb, then you're good.
note: A good general rule in computing is that things happen in powers of two. 2^10=1024, 2^12 = 4096.