interesting idea... i've never associated less heat with better performance.
I'll agree with a memory upgrade... most times, improving performance isn't a matter of hardware necessarily, unless you are a big gamer or use programs that need a ton of ram and processor speed.
Simply disabling unnecessary startup programs, processes and visual features will make a significant difference.
Try the msconfig utility, i'd leave msmessages ticked only because i have read that it can cause problems when unchecked.
Also try going to System properties, advanced, Performance (visual settings), and tick the button labeled 'best performance'. If you don't like how windows looks, go back and check 'use visual styles on windows and buttons' and if you don't want your desktop icons to have a blue background, check 'use drop shadows for icons on the desktop'. Mess with these check boxes until you are satisfied. The fewer the better.
Also try downloading and using TweakUI to further adjust performance options.