The info you've given isn't all that helpful.
Most people consider a 128mb card adeqaute for a film, which has a length of roughly 90-120mins.
Depending on the quality at which you recode the episodes (which will obvioulsy need to be done as at present they are 170mb in size) the amount of episodes you can fit will change dis-proportionately, basically, the better the quality, the fewer the episodes.
Most episodic shows seem to run for between 20-45mins. Im guessing you can fit around 2-5 episodes on one 128mb card.
Edit: Jebusss, i gotta learn to type quicker, five minutes after the post is posted??? and theres already a load of replies making mine irrelevant!