I have 2GB GSkill PC2-6400 Memory and want to go to 4GB

[clarkey01]

????

 

[JustaGeek]

No - to avoid potential problems.

It might work, but it is best to pair it up with exactly the same memory with identical timings, subtimings and voltage.

 

[imported_Willie]

I've got a pair of Buffalo Firestix DDR2-800 and a pair of Crucial Ballistix DDR2-800 sticks on my board...both sets playing quite happily @ 2.1V. Both OC'ing to 900MHz without difficulty or issues. Depends on your board, but your Asus shouldn't have many problems handling mixed RAM as long as they're rated for the same speed and voltage.

 

[Cutthroat]

I've mixed 2x1GB G-Skill 'HK' with 2x1GB 'HZ', as in my sig, works fine.