Ok but I''m still a bit cautious because this is what an OCZ tech said ....
"Upgrading the existing modules may not be possible due to incompatibility with currently manufactured modules. Running four modules of non-matched memory typically spells disaster. If you want 1GB of memory, it would be best to purchase 2x512MB modules and possibly sell your current memory or keep them for spares/backup.
I'd still like maybe a couple more opinions on this if anyone else wants to help clear this up for me. Thanks