Is this good memory?

No - Steer clear of Patriot.

Use either Certified {via MOBO} or Tested {via RAM Mfg}

Good companies: {Corsair, G.SKILL, Mushkin, Kingston, and Crucial}

:S What shoudl I do with the current 2gb ram? if I get different brand ram won't they be different ? can they be used together? (if so what ram do you recommend?)

note I'm planing to get a new mobo together with the ram (lga775)

Never mix DDR unless you REALLY know what you're doing. Find the EXACT DDR P/N and buy it - IF {PVS24G6400LLK} is what you already have then buy somemore.

Windows 32-bit {2GB Min/4GB Max} and Windows 64-bit {4GB Min/MOBO Max}.

I listed the best of the DDR Mfg, if you want post your MOBO model # and I'll list both Certified {via MOBO/XMP} and Tested {via RAM Mfg} DDR. Certified is required for XMP to function, but is no big deal.