the pictures included in ur post helped a lot. it seems that the system recognized both of ur memory sticks. as u can see, the "memory tab" indicates total of 2gb ram are running @ 200mhz, 4,4,4,12. the lower actual speed is caused by the mixture of sticks w/ different speed in ur system.why is vista displaying only 1gb ram (128 shared by the video card)? i have no clue since i don't know much about vista. follow butdie to try a linux livecd. if linux livecd shows only 1gb, that means i read cpu-z wrong. ;)
last but simply not the least, u may need to verify both of ur sticks have the same number of chips. sometimes, a stick w/ 4 chips doesn't like a stick w/ 8 chips.
good luck.