my question on RAM:

Is it possible to mix RAM modules that have different timing?
For example, i currently have these: http://www.newegg.com/Product/Produc...82E16820211066
but i also want to get these (rebate *drools*): http://www.newegg.com/Product/Produc...82E16820227198

existing modules: timing is 5-5-5-18, 1.8volts, CAS latency is 5.
new modules: timing is 4-4-4-15. 2.1volts, CAS latency is 4.

will having 4 gigs total, two of the old and two of the new, cause any conflicts or instabilities? they're both 800MHz DDR2s.