What resolution are you using in CrossFire? If you are using 1440x900, then make it 1024x768 because 1440x900 is too big and it takes huge ammounts of space. Also, make some other video settings lower if you still get too much space eaten by the videos.
Sony vegas,lol
And record with fraps,much better
First, get FRAPS or Camtasia. Are the best for you use.
After, just set your configuration during record and try see if don't lag you.
PM me, Ill send you a Full version/cracked version of fraps.