B grade simply means someone has bought it, didnt like it and returned it. Its then graded to see if its suitable for re-sale and thats about it. Just as an example i bought a 74gig 10,000rpm Raptor hard drive for something like £50 less than retail as it was returned but it still had all its packaging and disks. You get your usual rights to return for exchange or refund (just incase it is faulty) but the beauty is, if you need to return a B grade item it is always replaced with a new one. As for your processor, as its a P4 3.06gig (am i right in thinking its a 533 fsb, dont matter if you dont know) it will still move pretty quick but your ability to upgrade your graphics is strictly down to your mobo and what slots it has.
-------------------- Sarcasm is the lowest form of wit, but its all ive got!