can anyone recomend a screen capture and video editting software that is shareware/freeware, that doesnt grind my computer to a halt and can capture sound at the same time

For video editing, good old Windows Movie Maker.

Camtasia and pinnacle are both ok, for high end videos id recommend Sony Vegas.
for Screen Capture id recommend, Fraps or Xfire. Fraps is better than Xfire but uses a Griefers load of GB, like a gig every 10 mins or somethin. if your gunna use Fraps alot get an external harddrive.

All these are free if you go to the right places, lol.