Well Pentium4 800FSB 2.4Ghz too 3.2Ghz Systems tend too be the best for video editing but i do allot of Divxing and Virtual Dub editing and my Athlon 2500+ does the job very well and it's stable as a rock. plus it was cheaper then the 2.4Ghz Pentium system i was going to get.
The best Simple system for you would be -
CPU - AMD AthlonXP 2500+ 512k Cache 333FSB very strong and stable and
runs very cool !!!!
Motherboard - Nforce2 board 100% Stable and has a good onboard sound
Ram ? 2 Sticks of 512MB DDR 400 running them in Dual Channel - 512MB GEIL DDR400 case 2.5 there nice and cheap
Videocard - Geforce4Ti 42008x one head will be VGA the other DVI ? just get an adaptor for the DVI if you want to run 2 VGA Monitors
Hard drive ? 100GB should be fine so long as its a 7200RPM drive but i'm sure it is
Make sure you run windows XP SP1 on this system for better performance in video editing then win98 or win2k
This system should a very Stable and noticeably faster over the 800 Athlon that died other people here may advise you too grab a Pentium 4 system but its not really that much faster 15% isn?t worth the $100 extra you pay !
Another thing you may want to grab
Gknot its a very useful FREE divxing program that also comes with vid editing programs in the install

good luck and have fun building your new comp.
You can try the Matrix P650 in this system but for what your going to be doing its pointless getting this card or if you even want to save more money then insdead of getting the Geforce4ti42008x Card just grab a ATI9200 card because video Editing use's your CPU, RAM and Hard drive ... the videocard just sits there and looks pretty ! untill you want to play your stuff

... you should even be able too use the videocard you already have in the system that died !!! and upgrade too a new one if required!