No, Filming the screen won't give you a good quality.
Using a soft gives you the qualityy you need.
For example, you can use JING (free as far as i remember); it's quite
intuitive. Camtasia, for me, is the best but takes you money.
Once you start JING, you choose the part of the screen you want to record
(for a slideshow, it's of course full screen) Then uou choose to capture
Images or Video. Choose Video
3, 2, 1 ... TAke care to turn off microphone unless you need it