Be carefull with the old power supply, 300 w is min and 350 is better.
Not sure wy your mobo would be defaulted at 100 mhz. 133 FSB is faster, perhaps between 10 - 20% overall.
You did`nt mention your vid card?
Know FA about paste except be carefull not to drop any on mobo, this has happened before.
Nostradamus: "In the year 2002 naked alien women will descend to earth"
Change the jumper to 133mhz. Go to the articsilver website, to find the real way to apply thermal grease. The quick way is with a stiff piece of plastic(cut straight), coat both cpu metal center only and the contact area of the HSF. The grease should be very thinly coated on both parts, you are trying to get the thinest evenest coat possible.
To answer your question on 100 vs. 133mhz, yes, it is a big difference, more so if you OC your FSB. Also, if you do not have a 350+ watt high quality power supply(PSU), I suggest you get one before you build this system. If you are using your old Hard Drive(HDD), you need to reformat the drive and do a fresh install of your OS. Good Luck! I also have the same mobo and it has been flawless!
WHAT????? I CAN'T HEAR YOU OVER THE ROAR OF MY CASE FANS! YOU'LL HAVE TO SCREAM!