I think I understand what you are saying. Although I I may not be the best person to answer this.
Basically the drawing will be all screwy because the top left corner you are drawing from is changing do to different sized sprites.
One idea is to have a default size for all sprites for a character, say 64*64, even though the walk animation may only be 32*64.
The other is to have any spears/weapons/magic have their own sprite and be drawn on top of the character. This may make collisions for attacking easier.
The last idea would be to calculate the offset for the different sized sprites and add/subtract them from your drawing coordinates.
This I think is the best.
Here is a video to show what I think is going on for those with more expertise. http://www.youtube.com/watch?v=oJPe6cWIC-Q