Cool! - Thanks for all the great advice everyone - I had mistakenly thought my dell had a 450 PSU - because my old windows 98 box I had retired in my basement had a 450 W in it.
(and it won't seem to fit in the 8400 case)
I will blow it all out and re-check the fans again - I do need to upgrade but my car is now 11 years old and it's got to be replaced first...
Saw the new mega-comp in maximum pc's latest issue and it made me quite envious - but I don't think I'd shell out $7,800 for a computer ever when you can O/C a $2,000 one to run almost as good every time.
I'll report back my results after a good cleaning and fan check - and a another needed HDD defrag too.
Thanks!!