PCI-e >> AGP.
I googled around... and apparently there are AGP to PCI-e converters. I don't see WHY you would want to convert backwards... I think it would make more sense that... if you had a PCI-e slot, you would bother to actually buy a PCI-e card... *shrugs* Unless the cost of such a converter is minimal and you have an existing high-end AGP card...
Anyhew, I didn't find any converters specifically on sale... but I saw a couple of articles that claim they are coming out.
DDR3 >> DDR2
As per the
wikiAdvantages compared to DDR2
* Higher bandwidth (up to 1600 MHz)
* Performance increase at low power
* Longer battery life in laptops
* Enhanced low power features and thermal design
I believe I read somewhere that the DDR3 (and GDDR3) types of memory typically are faster, should perform better, and produce less heat (again better, cuz your system is less likely to overheat and/or it means you probably wouldn't have to worry about buying separate/additional fans).
I think both MSI and Sapphire are relatively reliable companies. I wouldn't recommend buying from a retail store tho. I suggest checking online sites like
www.newegg.com or
www.tigerdirect.com and what not. You might pay S&H, but in the long run, you will probably still get more for your money.
Ste